Chelated PSMA Inhibitors

ABSTRACT

Provided herein are compounds of Formula (I) or a pharmaceutically acceptable salt thereof. Also provided are compositions including a compound of Formula (I) together with a pharmaceutically acceptable carrier, and methods for imaging prostate cancer cells.

STATEMENT OF GOVERNMENT INTEREST

This application was supported by Contract No. HHSN261201500074C awarded by National Institutes of Health. The U.S. government has certain rights in the invention.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to small molecules having high affinity and specificity to prostrate-specific membrane antigen (PSMA) and methods of using them for diagnostic and therapeutic purposes.

Summary of the Related Art

Prostate-specific membrane antigen (PSMA) is uniquely overexpressed on the surface of prostate cancer cells as well as in the neovasculature of a variety of solid tumors. As a result, PSMA has attracted attention as a clinical biomarker for detection and management of prostate cancer. Generally, these approaches utilize an antibody specifically targeted at PSMA to direct imaging or therapeutic agents. For example, ProstaScint (Cytogen, Philadelphia, Pa.), which has been approved by the FDA for the detection and imaging of prostate cancer, utilizes an antibody to deliver a chelated radioisotope (Indium-111). However, it is now recognized that the ProstaScint technology is limited to the detection of dead cells and therefore its clinical relevance is questionable.

The success of cancer diagnosis and therapy using antibodies is limited by challenges such as immunogenicity and poor vascular permeability. In addition, large antibodies bound to cell-surface targets present a barrier for subsequent binding of additional antibodies at neighboring cell-surface sites resulting in a decreased cell-surface labeling.

In addition to serving as a cell-surface target for antibodies delivering diagnostic or therapeutic agents, a largely overlooked and unique property of PSMA is its enzymatic activity. That is, PSMA is capable of recognizing and processing molecules as small as dipeptides. Despite the existence of this property, it has been largely unexplored in terms of the development of novel diagnostic and therapeutic strategies. There are a few recent examples in the literature that have described results in detecting prostate cancer cells using labeled small-molecule inhibitors of PSMA.

Certain phosphoramidate and phosphate PSMA inhibitors have been described in U.S. Pat. Nos. 7,696,185, 8,293,725, RE42,275, and in U.S. Patent Application Publication Nos. US-2014-0241985-A1 and US-2016-0030605-A1.

SUMMARY OF THE INVENTION

Provided herein are imaging diagnostics and therapeutics for prostate cancer that capitalize on the potency and specific affinity of small-molecule inhibitors to PSMA. The diagnostic agents can be used to monitor and stratify patients for treatment with appropriate therapeutic agents.

Accordingly, in one aspect the present disclosure provides compounds of Formula (I*)

or a pharmaceutically acceptable salt thereof, wherein

-   -   L¹ and L² are independently a divalent linking group;     -   R is a chelating agent optionally chelating a therapeutic         radioisotope or a PET-active, SPECT-active, or MRI-active         radioisotope;     -   each R¹ and R² are independently hydrogen, C₁-C₆ alkyl or a         protecting group; and     -   X is an albumin bind moiety.

In another aspect, the present disclosure provides compounds of Formula (I)

or a pharmaceutically acceptable salt thereof, wherein

-   -   L¹ and L² are independently a divalent linking group;     -   R is a chelating agent optionally chelating a therapeutic         radioisotope or a PET-active, SPECT-active, or MRI-active         radioisotope; and     -   each R¹ and R² are independently hydrogen, C₁-C₆ alkyl or a         protecting group.

In another aspect the present disclosure provides pharmaceutical compositions comprising a compound of the preceding aspect and a pharmaceutically acceptable carrier.

In another aspect the present disclosure provides methods for imaging one or more prostate cancer cells or tumor-associated vasculature in a patient comprising administering to the patient a compound or a pharmaceutical composition of either of the preceding aspects.

All publicly available documents recited in this application are hereby incorporated by reference in their entirety to the extent their teachings are not inconsistent with the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is shows uptake of CTT1403 in PC3-PSMA-positive cells. Specific uptake was determined by subtracting uptake in PC3-PSMA-positive cells pre-incubated with 2-PMPA as a blocking agent from uptake in unblocked cells.

FIG. 2 shows biodistribution of CTT1403 in PC3-PIP and PC3-WT tumor-bearing mice at 4 and 24 hours as determined by radioactivity per gram of tissue.

FIG. 3 shows therapeutic efficacy of CTT1403 (9 animals) vs control (7 animals) in mice bearing PSMA-positive (PSMA+) human tumor xenografts. Mice were injected when starting tumor volumes reached 10-20 mm³.

FIG. 4 shows therapeutic efficacy of CTT1403 (Comparison of experiment 1 and 2) vs control in mice bearing PSMA+ human tumor xenografts. Mice were injected when starting tumor volumes reached 10-20 mm³.

FIG. 5 shows expanded scale of FIG. 4. Therapeutic Efficacy of CTT1403 (2 experiments) vs control in mice bearing PSMA+ human tumor xenografts.

FIG. 6 shows Kaplan Meier Survival Plots of CTT1403 Treated Mice. Comparison of repeat therapy (8 animals) experiments (as of day 42 of experiment) as compared to untreated control mice (17 animals). Median survival times are 42 days for control group and 55 days for expt 1 CTT1403 group, post tumor implant. This represents a 14% and 31% increase in survival, respectively. No animal has been sacrificed for the expt 2 CTT1403 treatment group as of day 42 of the experiment.

DETAILED DESCRIPTION OF THE INVENTION

In one aspect, the present disclosure provides compounds useful as PET imaging diagnostics and radiotherapeutic agents for prostate cancer that capitalize on the potency and specific affinity of small-molecule inhibitors to PSMA.

In embodiment 1* of the first aspect, the compounds have structural Formula (I*)

or a pharmaceutically acceptable salt thereof, wherein

-   -   L¹ and L² are independently a divalent linking group;     -   R is a chelating agent optionally chelating a therapeutic         radioisotope or a PET-active, SPECT-active, or MRI-active         radioisotope;     -   each R¹ and R² are independently hydrogen, C₁-C₆ alkyl or a         protecting group; and X is an albumin bind moiety.

Numerous albumin binding moieties useful in the compounds and methods of the invention are known in the art and include, for example, moieties disclosed and referred to in the following (each of which are incorporated herein by reference): Ghuman et al., “Structural Basis of the Drug-binding Specificity of Human Serum Albumin,” Journal of Molecular Biology, 353(1), 14 Oct. 2005, 38-52; Carter, D. C. and Ho, J. X. (1994) “Structure of serum albumin,” Adv. Protein Chem., 45, 153-203; Curry, S. (2009) “Lessons from the crystallographic analysis of small molecule binding to human serum albumin,” Drug Metab. Pharmacokinet., 24, 342-357; Kratochwil, N. A. et al. (2002) “Predicting plasma protein binding of drugs: a new approach,” Biochem. Pharmacol., 64, 1355-1374; Zsila et al. (2011) “Evaluation of drug-human serum albumin binding interactions with support vector machine aided online automated docking,” Bioimformatics 27(13), 1806-1813; Elsadek et al., J Control Release., “Impact of albumin on drug delivery—new applications on the horizon,” 2012 Jan. 10; 157(1):4-28; Nemati et al., “Assessment of Binding Affinity between Drugs and Human Serum Albumin Using Nanoporous Anodic Alumina Photonic Crystals,” Anal Chem. 2016 Jun. 7; 88(11):5971-80; Larsen, M. T. et al., “Albumin-based drug delivery: harnessing nature to cure disease,” Mol Cell. Ther., 2016, Feb. 27; 4:3; Howard, K. A., “Albumin: the next-generation delivery technology,” Ther. Deliv., 2015, March; 6(3):265-8; Sleep D. et al., “Albumin as a versatile platform for drug half-life extension,” Biochim. Biophys. Acta., 2013, December; 1830(12):5526-34; Sleep, D., “Albumin and its application in drug delivery,” Expert Opin. Drug Deliv., 2015, May; 12(5):793-812; Qi, J et al., “Multidrug Delivery Systems Based on Human Serum Albumin for Combination Therapy with Three Anticancer Agents,” Mol. Pharm., 2016, Aug. 8., Article ASAP Epub ahead of print; Karimi M. et al., “Albumin nanostructures as advanced drug delivery systems,” Expert Opin. Drug Deliv., 2016, June 3:1-15, Article ASAP Epub ahead of print; Gou, Y. et al., “Developing Anticancer Copper(II) Pro-drugs Based on the Nature of Cancer Cells and the Human Serum Albumin Carrier IIA Subdomain,” Mol. Pharm., 2015, Oct. 5; 12(10):3597-609; Yang, F. et al., “Interactive associations of drug-drug and drug-drug-drug with IIA subdomain of human serum albumin,” Mol. Pharm., 2012, Nov. 5; 9(11):3259-65; Agudelo, D. et al., “An overview on the delivery of antitumor drug doxorubicin by carrier proteins,” Int. J. Biol. Macromol., 2016, July; 88:354-60; Durandin, N. A. et al., “Quantitative parameters of complexes of tris(1-alkylindol-3-yl)methylium salts with serum albumin: Relevance for the design of drug candidates,” J. Photochem. Photobiol. B., 2016, Jul. 18; 162:570-576; Khodaei, A. et al., “Interactions Between Sirolimus and Anti-Inflammatory Drugs: Competitive Binding for Human Serum Albumin,” Adv. Pharm. Bull., 2016, June; 6(2):227-33; Gokara, M. et al., “Unravelling the Binding Mechanism and Protein Stability of Human Serum Albumin while Interacting with Nefopam Analogues: A Biophysical and Insilco approach,” J. Biomol. Struct. Dyn., 2016, July 25:1-44; Zhang, H. et al., “Affinity of miriplatin to human serum albumin and its effect on protein structure and stability,” Int. J. Biol. Macromol., 2016, Jul. 22; 92:593-599; Bijelic, A. et al., “X-ray Structure Analysis of Indazolium trans-[Tetrachlorobis(1H-indazole)ruthenate(III)] (KP1019) Bound to Human Serum Albumin Reveals Two Ruthenium Binding Sites and Provides Insights into the Drug Binding Mechanism,” J. Med. Chem., 2016, Jun. 23; 59(12):5894-903; Fasano, M. et al., “The Extraordinary Ligand Binding Properties of Human Serum Albumin,” Life, 57(12): 787-796. Albumin binding is also utilized in many known drugs, such as warfarin, lorazepam, and ibuprofen. In some embodiments according to the invention, X is

In embodiment I₁ of this first aspect, the compounds have structural formula (I):

or a pharmaceutically acceptable salt thereof, wherein

-   -   L¹ and L² are independently a divalent linking group;     -   R is a chelating agent optionally chelating a therapeutic         radioisotope or a PET-active, SPECT-active, or MRI-active         radioisotope; and     -   each R¹ and R² are independently hydrogen, C₁-C₆ alkyl or a         protecting group.

Divalent linking groups include groups of the formula, —(C₀-C₁₀ alkyl-Q)₀₋₁-C₀-C₁₀ alkyl-, wherein Q is a bond, aryl (e.g., phenyl), heteroaryl, C₃-C₅ cycloalkyl, or heterocyclyl; and no more than one methylene in each alkyl group is optionally and independently replaced by —O—, —S—, —N(R⁰⁰)—, —C(H)═C(H)—, —C≡C—, —C(O)—, —S(O)—, —S(O)₂—, —P(O)(OR⁰⁰)—, —OP(O)(O R⁰⁰)—, —P(O)(OR⁰⁰)O—, —N(R⁰⁰)P(O)(OR⁰⁰)—, —P(O)(OR⁰⁰)N(R⁰⁰)—, —OP(O)(OR⁰⁰)O—, —OP(O)(O R⁰⁰)N(R⁰⁰)—, —N(R⁰⁰)P(O)(OR⁰⁰)O—, —N(R⁰⁰)P(O)(OR⁰⁰)N(R⁰⁰)—, —C(O)O—, —C(O)N(R⁰⁰)—, —OC (O)—, —N(R⁰⁰)C(O)—, —S(O)O—, —OS(O)—, —S(O)N(R⁰⁰)—, —N(R⁰⁰)S(O)—, —S(O)₂O—, —OS(O)₂—, —S(O)₂N(R⁰⁰)—, —N(R⁰⁰)S(O)₂—, —OC(O)O—, —OC(O)N(R⁰⁰)—, —N(R⁰⁰)C(O)O—, —N(R⁰⁰)C(O)N(R⁰⁰)—, —OS(O)O—, —OS(O)N(R⁰⁰)—, —N(R⁰⁰)S(O)O—, —N(R⁰⁰)S(O)N(R⁰⁰)—, —OS(O)₂O—, —OS(O)₂N(R⁰⁰)—, —N(R⁰⁰)S(O)₂O—, or —N(R⁰⁰)S(O)₂N(R⁰⁰)—, wherein each R⁰⁰ is independently hydrogen or C₁-C₆ alkyl.

In other embodiments, divalent linking groups is selected from one of the following groups of the formula, wherein in each instance, the *-end is attached to the chelating agent:

-   (a) *—(OCH₂CH₂)_(n)—, wherein n is 1-20 (e.g., 4-12, or 4, or 8, or     12); -   (b) —(C(O)—(CH₂)₀₋₁—CH(R¹)N(R²))_(m)—*, wherein     -   m is 1-8;     -   each R¹ is independently the side chain of a natural or         unnatural amino acid (e.g., each R¹ is independently hydrogen,         C₁-C₆alkyl, aryl, heteroaryl, arylC₁-C₆alkyl, or         heteroarylC₁-C₆alkyl, wherein the alkyl, arylalkyl, and         heteroarylalkyl groups are optionally substituted with 1, 2, 3,         4, or 5 R¹¹ groups, wherein each R¹¹ is independently halo,         cyano, —OR¹², —SR¹², —N(R¹²)₂, —C(O)OR¹², —C(O)N(R¹²)₂,         —N(R¹²)C(═NR¹²)N(R¹²)₂, or C₁-C₆alkyl, wherein each R¹² is         independently hydrogen or C₁-C₆alkyl);     -   each R² is independently hydrogen or taken together with R¹         within the same residue to form a heterocyclyl (e.g., having         5-members); -   (c) —(C(O)(CH₂)_(p)—(C(O))₀₋₁—NH)—*, wherein p is 1-30 (e.g., p is     1-7) (e.g., 6-aminohexanoic acid, —C(O)(CH₂)₅NH—*); -   (d) —(C(O)—(CH₂)_(r)-phenyl-(G)₀₋₁-(CH₂)_(q)—(C(O))₀₋₁—NH)—*,     wherein G is —O— or —N(H)—, -r and q are each independently 0-30     (e.g., 0-20; or 0-10, or 0-6, or 1-6) (e.g.,     —(C(O)-phenyl-N(H)(CH₂)_(q)—(C(O))₀₋₁—NH)—*, wherein q is 1-6; or     —(C(O)—(CH₂)_(r)-phenyl-(CH₂)_(q)—NH)—*, wherein r and q are each     independently 0-6; or the two substituents on the phenyl are para to     one another, such as in 4-aminomethylbenzoic acid,

where r is 0, and q is 1; or as in 4-aminoethylbenzoic acid,

where r is 0 and q is 2); or

-   (e)

-   -   wherein         -   L² is —(CH₂)_(t)N(H)—*, wherein t is 1 to 30; and         -   L³ is #—(CH₂)_(u)—C(O)—, #—(CH₂)_(u)—Z—Y—C(O)—,             #—C(O)—(CH₂)_(u)—C(O)— or #—C(O)—(CH₂)_(u)—Z—Y—C(O)—,             wherein             -   the # end of L³ is attached to the dibenzocyclooctyne or                 triazolyl group above;             -   u is 1 to 30;             -   Y is —(CH₂)_(u)— or **—CH₂CH₂—(OCH₂CH₂)_(n)—, wherein                 -   u is 1 to 30;                 -   n is 1-20 (e.g., 4-12, or 4, or 8, or 12); and                 -   the **-end is attached to Z; and             -   Z is —C(O)O—, —C(O)N(R⁰⁰)—, —OC(O)—, —N(R⁰⁰)C(O)—,                 —S(O)₂N(R⁰⁰)—, —N(R⁰⁰)S(O)₂—, —OC(O)O—, —OC(O)N(R⁰⁰)—,                 —N(R⁰⁰)C(O)O—, or —N(R⁰⁰)C(O)N(R⁰⁰)—, wherein each R⁰⁰                 is independently hydrogen or C₁-C₆ alkyl;

-   (f)

-   -   wherein         -   L² is —(CH₂)_(t)N(H)—*, wherein t is 1 to 30; and         -   L³ is #—(CH₂)_(u)—C(O)—, #—(CH₂)_(u)—Z—Y—C(O)—,             #—C(O)—(CH₂)_(u)—C(O)— or #—C(O)—(CH₂)_(u)—Z—Y—C(O)—,             wherein             -   the # end of L³ is attached to the dibenzocyclooctyne or                 triazolyl group above;             -   u is 1 to 30;             -   Y is —(CH₂)_(u)— or **—CH₂CH₂—(OCH₂CH₂)_(n)—, wherein                 -   u is 1 to 30;                 -   n is 1-20 (e.g., 4-12, or 4, or 8, or 12); and                 -   the **-end is attached to Z; and             -   Z is —C(O)O—, —C(O)N(R⁰⁰)—, —OC(O)—, —N(R⁰⁰)C(O)—,                 —S(O)₂N(R⁰⁰)—, —N(R⁰⁰)S(O)₂—, —OC(O)O—, —OC(O)N(R⁰⁰)—,                 —N(R⁰⁰)C(O)O—, or —N(R⁰⁰)C(O)N(R⁰⁰)—, wherein each R⁰⁰                 is independently hydrogen or C₁-C₆ alkyl;

-   (g)

-   -   wherein         -   L² is —(CH₂)_(t)N(H)—*, wherein t is 1 to 30; and         -   L³ is #—(CH₂)_(u)—C(O)—, #—(CH₂)_(u)—Z—Y—C(O)—,             #—C(O)—(CH₂)_(u)—C(O)— or #—C(O)—(CH₂)_(u)—Z—Y—C(O)—,             wherein             -   the # end of L³ is attached to the dibenzocyclooctyne or                 triazolyl group above;             -   u is 1 to 30;             -   Y is —(CH₂)_(u)— or **—CH₂CH₂—(OCH₂CH₂)_(n)—, wherein                 -   u is 1 to 30;                 -   n is 1-20 (e.g., 4-12, or 4, or 8, or 12); and                 -   the **-end is attached to Z; and             -   Z is —C(O)O—, —C(O)N(R⁰⁰)—, —OC(O)—, —N(R⁰⁰)C(O)—,                 —S(O)₂N(R⁰⁰)—, —N(R⁰⁰)S(O)₂—, —OC(O)O—, —OC(O)N(R⁰⁰)—,                 —N(R⁰⁰)C(O)O—, or —N(R⁰⁰)C(O)N(R⁰⁰)—, wherein each R⁰⁰                 is independently hydrogen or C₁-C₆ alkyl;

-   h)

-   -   wherein         -   L² is —(CH₂)_(t)N(H)—*, wherein t is 1 to 30; and         -   L³ is #—(CH₂)_(u)—C(O)—, #—(CH₂)_(u)—Z—Y—C(O)—,             #—C(O)—(CH₂)_(u)—C(O)— or #—C(O)—(CH₂)_(u)—Z—Y—C(O)—,             wherein             -   the # end of L³ is attached to the dibenzocyclooctyne or                 triazolyl group above;             -   u is 1 to 30;             -   Y is —(CH₂)_(u)— or **—CH₂CH₂—(OCH₂CH₂)_(n)—, wherein                 -   u is 1 to 30;                 -   n is 1-20 (e.g., 4-12, or 4, or 8, or 12); and                 -   the **-end is attached to Z; and             -   Z is —C(O)O—, —C(O)N(R⁰⁰)—, —OC(O)—, —N(R⁰⁰)C(O)—,                 —S(O)₂N(R⁰⁰)—, —N(R⁰⁰)S(O)₂—, —OC(O)O—, —OC(O)N(R⁰⁰)—,                 —N(R⁰⁰)C(O)O—, or —N(R⁰⁰)C(O)N(R⁰⁰)—, wherein each R⁰⁰                 is independently hydrogen or C₁-C₆ alkyl;

-   (i)

-   -   wherein         -   L² is —(CH₂)_(t)N(H)—*, wherein t is 1 to 30; and         -   L³ is #—(CH₂)_(u)—C(O)—, #—(CH₂)_(u)—Z—Y—C(O)—,             #—C(O)—(CH₂)_(u)—C(O)— or #—C(O)—(CH₂)_(u)—Z—Y—C(O)—,             wherein             -   the # end of L³ is attached to the dibenzocyclooctyne or                 triazolyl group above,             -   u is 1 to 30;             -   Y is —(CH₂)_(u)— or **—CH₂CH₂—(OCH₂CH₂)_(n)—, wherein                 -   u is 1 to 30;                 -   n is 1-20 (e.g., 4-12, or 4, or 8, or 12); and                 -   the **-end is attached to Z; and             -   Z is —C(O)O—, —C(O)N(R⁰⁰)—, —OC(O)—, —N(R⁰⁰)C(O)—,                 —S(O)₂N(R⁰⁰)—, —N(R⁰⁰)S(O)₂—, —OC(O)O—, —OC(O)N(R⁰⁰)—,                 —N(R⁰⁰)C(O)O—, or —N(R⁰⁰)C(O)N(R⁰⁰)—, wherein each R⁰⁰                 is independently hydrogen or C₁-C₆ alkyl;

-   (j)

-   -   wherein         -   L² is —(CH₂)_(t)N(H)—*, wherein t is 1 to 30; and         -   L³ is #—(CH₂)_(u)—C(O)—, #—(CH₂)_(u)—Z—Y—C(O)—,             #—C(O)—(CH₂)_(u)—C(O)— or #—C(O)—(CH₂)_(u)—Z—Y—C(O)—,             wherein             -   the # end of L³ is attached to the dibenzocyclooctyne or                 triazolyl group above;             -   u is 1 to 30;             -   Y is —(CH₂)_(u)— or **—CH₂CH₂—(OCH₂CH₂)_(n)—, wherein                 -   u is 1 to 30;                 -   n is 1-20 (e.g., 4-12, or 4, or 8, or 12); and                 -   the **-end is attached to Z; and             -   Z is —C(O)O—, —C(O)N(R⁰⁰)—, —OC(O)—, —N(R⁰⁰)C(O)—,                 —S(O)₂N(R⁰⁰)—, —N(R⁰⁰)S(O)₂—, —OC(O)O—, —OC(O)N(R⁰⁰)—,                 —N(R⁰⁰)C(O)O—, or —N(R⁰⁰)C(O)N(R⁰⁰)—, wherein each R⁰⁰                 is independently hydrogen or C₁-C₆ alkyl;

-   and (k) combinations of the preceding, wherein in each instance, the     *-end is attached to the chelating agent, such as:     -   (i) —(CH₂CH₂O)_(n)—(C(O)(CH₂)_(p)—(C(O))₀₋₁—NH)—*, where n and p         are as defined above (e.g., n is 4 and p is 6);     -   (ii) —(CH₂CH₂O)_(n)—(C(O)—(CH₂)₀₋₁—CH(R¹)N(R²))_(m)—*, where R¹,         R², n and m are as defined above (e.g., n is 4 and m is 2);     -   (iii)         —(CH₂CH₂O)_(n)—(C(O)—(CH₂)_(r)-phenyl-(G)₀₋₁-(CH₂)_(q)—(C(O))₀₋₁—NH)—*,         where G, n, q, and r are as defined above (e.g., n is 4, q is 1,         and r is 0);     -   (iv)         —(C(O)—(CH₂)₀₋₁—CH(R¹)N(R²))_(m)—(C(O)(CH₂)_(p)—(C(O))₀₋₁—NH)—*,         where R¹, R², m and p are as defined above (e.g., m is 2 and p         is 6);     -   (v)         —(C(O)—(CH₂)₀₋₁—CH(R¹)N(R²))_(m)—(C(O)—(CH₂)_(r)-phenyl-(G)₀₋₁-(CH₂)_(q)—(C(O))₀₋₁—NH)—*,         where G, R¹, R², m, q, and r are as defined above (e.g., m is 2,         q is 1, and r is 0; or m is 2, q is 2, and r is 0);     -   (vi)         —(C(O)(CH₂)_(p)—(C(O))₀₋₁—NH)—(C(O)—(CH₂)_(r)-phenyl-(G)₀₋₁-(CH₂)_(q)—(C(O))₀₋₁—NH)—*,         where G, p, q, and r are as defined above (e.g., p is 6, q is 1,         and r is 0; p is 6, q is 2, and r is 0; p is 5, q is 1, and r is         0; or p is 5, q is 2, and r is 0);     -   (vii)         —(C(O)(CH₂)_(p)—(C(O))₀₋₁—NH)—(C(O)—(CH₂)₀₋₁—CH(R¹)N(R²))_(m)—*,         where R¹, R² m and p are as defined above (e.g., m is 2 and p is         6);     -   (viii)         —(C(O)—(CH₂)_(r)-phenyl-(G)₀₋₁-(CH₂)_(q)—(C(O))₀₋₁—NH)—(C(O)—(CH₂)₀₋₁—CH(R¹)N(R²))_(m)—*,         where G, R¹, R², m, q, and r are as defined above (e.g., m is 2,         q is 1, and r is 0; or m is 2, q is 2, and r is 0);     -   (ix)         —(C(O)—(CH₂)_(r)-phenyl-(G)₀₋₁-(CH₂)_(q)—(C(O))₀₋₁—NH)—(C(O)(CH₂)_(p)—(C(O))₀₋₁—NH)—*,         where G, p, q, and r are as defined above (e.g., p is 6, q is 1,         and r is 0; p is 6, q is 2, and r is 0; p is 5, q is 1, and r is         0; or p is 5, q is 2, and r is O);     -   (x) —(C(O)(CH₂)_(p)—(C(O))₀₋₁—NH)—(CH₂CH₂O)_(n)—*, where n and p         are as defined above (e.g., n is 4 and p is 6);     -   (xi) —(C(O)—(CH₂)₀₋₁—CH(R¹)N(R²))_(m)—(CH₂CH₂O)_(n)—*, where R¹,         R², n and m are as defined above (e.g., n is 4 and m is 2); and     -   (xii)         —(C(O)—(CH₂)_(r)-phenyl-(G)₀₋₁-(CH₂)_(q)—(C(O))₀₋₁—NH)—(CH₂CH₂O)_(n)—*,         where G, n, q, and r are as defined above (e.g., n is 4, q is 1,         and r is 0; n is 4, q is 2, and r is 0);     -   (xiii) —(C(O)(CH₂)_(p)N(H)C(O)(CH₂)_(p)NH—)*, where each p is         independently as defined above (e.g., each p is 5,         —C(O)(CH₂)₅NH—C(O)(CH₂)₅NH—*);     -   (xiv) a covalent bond.

In other embodiments, divalent linking groups is selected from one of the following groups of the formula, wherein in each instance, the *-end is attached to the chelating agent:

-   -   (xv) —(C(O)(CH₂)_(p)—(C(O))₀₋₁—NH)—*, wherein p is 1-7, (e.g.,         6-aminohexanoic acid, —C(O)(CH₂)₅NH—*);     -   (xvi) —(C(O)—(CH₂)_(r)-phenyl-(G)₀₋₁-(CH₂)_(q)—(C(O))₀₋₁—NH)—*,         wherein G is —N(H)—, r is 0-6 (e.g., 0-3, or 0-2, or 0, or 1, or         2, or 1-6), q is 1-6 (e.g., 1-3, or 1-2, or 1, or 2) (e.g., the         two substituents on the phenyl are para to one another, such as         in 4-aminomethylbenzoic acid,

where r is 0 and q is 1; or as in 4-aminoethylbenzoic acid,

where r is 0 and q is 2); or

-   -   (xvii)         —(C(O)(CH₂)_(p)—(C(O))₀₋₁—NH)—(C(O)—(CH₂)_(r)-phenyl-(G)₀₋₁-(CH₂)_(q)—(C(O))₀₋₁—NH)—*,         where G, p, q, and r are as defined above (e.g., p is 6, q is 1,         and r is 0; p is 6, q is 2, and r is 0; p is 5, q is 1, and r is         0; or p is 5, q is 2, and r is O);     -   (xviii)         —(C(O)—(CH₂)_(r)-phenyl-(G)₀₋₁-(CH₂)_(q)—(C(O))₀₋₁—NH)—(C(O)(CH₂)_(p)—(C(O))₀₋₁—NH)—*,         where G, p, q, and r are as defined above (e.g., p is 6, q is 1,         and r is 0; p is 6, q is 2, and r is 0; p is 5, q is 1, and r is         0; or p is 5, q is 2, and r is O);     -   (xix) —(C(O)(CH₂)_(p)N(H)C(O)(CH₂)_(p)NH—)*, where each p is         independently as defined above (e.g., each p is 5,         —C(O)(CH₂)₅NH—C(O)(CH₂)₅NH—);     -   (xx) a covalent bond.

In other embodiments, divalent linking groups is selected from one of the following groups of the formula, wherein in each instance, the *-end is attached to the chelating agent:

-   -   (xxi) —(C(O)(CH₂)_(p)—(C(O))₀₋₁—NH)—*, wherein p is 4-6, (e.g.,         6-aminohexanoic acid, —C(O)(CH₂)₅NH—*);     -   (xxii) —(C(O)—(CH₂)_(r)-phenyl-(G)₀₋₁-(CH₂)_(q)—(C(O))₀₋₁—NH)—*,         wherein G is —N(H)—, r is 0-6 and q is 1-3 (e.g., the two         substituents on the phenyl are para to one another, such as in         4-aminomethylbenzoic acid,

where q is 1; or as in 4-aminoethylbenzoic acid,

where q is 2); or

-   -   (xxiii)         —(C(O)(CH₂)_(p)—(C(O))₀₋₁—NH)—(C(O)—(CH₂)_(r)-phenyl-(G)₀₋₁-(CH₂)_(q)—(C(O))₀₋₁—NH)—*,         where p, q, and r are as defined above (e.g., p is 6, q is 1,         and r is 0; p is 6, q is 2, or r is 0; p is 5, q is 1, and r is         0; or p is 5, q is 2, and r is 0);     -   (xxiv)         —(C(O)—(CH₂)_(r)-phenyl-(G)₀₋₁-(CH₂)_(q)—(C(O))₀₋₁—NH)—(C(O)(CH₂)_(p)—(C(O))₀₋₁—NH)—*,         where G, p, q, and r are as defined above (e.g., p is 6, q is 1,         and r is 0; p is 6, q is 2, and r is 0; p is 5, q is 1, and r is         0; or p is 5, q is 2, and r is O);     -   (xxv) —(C(O)(CH₂)_(p)N(H)C(O)(CH₂)_(p)NH—)*, where each p is         independently as defined above (e.g., each p is 5,         —C(O)(CH₂)₅NH—C(O)(CH₂)₅NH—*);     -   (xxvi) a covalent bond.

In other embodiments, divalent linking groups is selected from one of the following groups of the formula, wherein in each instance, the *-end is attached to the chelating agent:

(ix) a covalent bond

In embodiment I₂, the compounds are of embodiment I₁, wherein

-   -   L¹ is a moiety of the formula         L^(1A)-NH—CH₂CH₂—(OHC₂CH₂)_(y)—CO—, wherein         -   y is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12; and         -   L^(1A) is a divalent linking group.

In embodiment I_(2a), the compounds are of embodiment I₂ wherein y is selected from one of the following groups (1a)-(1x):

(1a) 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12. (1b) 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10. (1c) 1, 2, 3, 4, 5, 6, 7 or 8. (1d) 1, 2, 3, 4, 5 or 6. (1e) 1, 2, 3 or 4. (1f) 1 or 2. (1g) 6, 7, 8, 9, 10, 11 or 12. (1h) 6, 7, 8, 9 or 10. (1i) 3, 4, 5, 6, 7 or 8. (1j) 2, 4, 6, 8, 10 or 12. (1k) 2, 4, 6 or 8. (1l) 1, 3, 5, 7, 9 or 11. (1m) 1. (1n) 2. (1o) 3. (1p) 4. (1q) 5. (1r) 6. (1s) 7. (1t) 8. (1u) 9. (1v) 10. (1w) 11. (1x) 12.

In embodiment I₃, the compounds are of embodiment I₁ or I₂, wherein

-   -   L² is a group of the formula

-   -   wherein         -   m is 1, 2, 3, or 4;         -   each n is independently 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or             12;         -   provided that m·(n+2) is greater than or equal to 3 and less             than or equal to 21.

In embodiment I_(3a), the compounds are of embodiment I₃ wherein m is selected from one of the following groups (2a)-(2o):

(2a) 1, 2, 3 or 4. (2b) 1, 2 or 3. (2c) 1 or 2. (2d) 1. (2e) 2, 3 or 4. (2f) 1 or 3. (2g) 2 or 4. (2h) 1 or 2. (21) 2 or 3. (2j) 3 or 4. (2k) 1 or 4. (21) 1. (2m) 2. (2n) 3. (2o) 4.

In embodiment I_(3b), the compounds are of embodiment I₃ or I_(3a) wherein each n is independently selected from one of the following groups (3a)-(3x):

(3a) 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12. (3b) 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10. (3c) 1, 2, 3, 4, 5, 6, 7 or 8. (3d) 1, 2, 3, 4, 5 or 6. (3e) 1, 2, 3 or 4. (3f) 1 or 2. (3g) 6, 7, 8, 9, 10, 11 or 12. (3h) 6, 7, 8, 9 or 10. (3i) 3, 4, 5, 6, 7 or 8. (3j) 2, 4, 6, 8, 10 or 12. (3k) 2, 4, 6 or 8. (31) 1, 3, 5, 7, 9 or 11. (3m) 1. (3n) 2. (3o) 3. (3p) 4. (3q) 5. (3r) 6. (3s) 7. (3t) 8. (3u) 9. (3v) 10. (3w) 11. (3x) 12.

In embodiment I₄, the compounds are of any of embodiments I₁-I₃, wherein the compound has the structure of Formula I*:

or a pharmaceutically acceptable salt thereof, wherein L¹, L², R, R¹ and R² are as described herein.

In Formula (I*), 1*, 2*, and 3* are chiral centers that are independently racemic (rac) or in the S or R stereoconfiguration. Thus, compounds according to this aspect include those with the following combinations of stereoconfigurations, and mixtures thereof:

$\begin{matrix} 1^{*} & 2^{*} & 3^{*} \\ S & S & R \\ S & S & R \\ S & R & S \\ R & {rac} & R \end{matrix}$ $\begin{matrix} 1^{*} & 2^{*} & 3^{*} \\ R & S & S \\ S & R & R \\ R & S & R \\ S & S & {rac} \end{matrix}$ $\begin{matrix} 1^{*} & 2^{*} & 3^{*} \\ R & R & S \\ R & R & R \\ {rac} & S & S \\ S & R & {rac} \end{matrix}$ $\begin{matrix} 1^{*} & 2^{*} & 3^{*} \\ {rac} & S & R \\ {rac} & R & S \\ {rac} & R & R \\ R & S & {rac} \end{matrix}$ $\begin{matrix} 1^{*} & 2^{*} & 3^{*} \\ S & {rac} & S \\ S & {rac} & R \\ R & {rac} & S \\ R & R & {rac} \end{matrix}$

In embodiment I₅, the compounds of embodiment I₁ have the structure of Formula (Ia):

or a pharmaceutically acceptable salt thereof, wherein L¹, R, R¹ and R² are as described herein.

In embodiment I₆, the compounds of embodiment I₁ have the structure of Formula (Ib):

or a pharmaceutically acceptable salt thereof, wherein

y is 2, 3, 4, 5 or 6;

L^(1A) is a divalent linker; and

R, R¹ and R² are as described herein.

In embodiment I_(6a), the compounds are of embodiment I₁ having the structure of Formula (Ib), or the compounds are of embodiment I₂, wherein L^(1A) is:

wherein

-   -   w is 1, 2, 3, 4, 5 or 6;     -   ring A is heterocyclic;     -   and L^(1B) is a divalent linker.

In embodiment I_(6b), the compounds are of embodiment I_(6a) wherein L^(1B) is: C₁-C₆alkyl-NH—.

In embodiment I_(6c), the compounds are of embodiment I₁ having the structure of Formula (Ib), or the compounds are of embodiment I₂, wherein L^(1A) is:

wherein

-   -   w is 1, 2, 3, 4, 5 or 6;     -   ring A₁ is heterocyclic; and     -   L^(1B) is a divalent linker.

In embodiment I_(6a), the compounds are of embodiment I_(6a) wherein L^(1B) is: C₁-C₆alkyl-NH—.

In embodiment I_(6e), the compounds are of embodiment I₁ having the structure of Formula (Ib), or the compounds are of embodiment I₂, wherein L^(1A) is:

wherein

-   -   w is 1, 2, 3, 4, 5 or 6;     -   ring A₁ is heterocyclic; and     -   L^(1B) is a divalent linker.

In embodiment I_(6f), the compounds are of embodiment I_(6a) wherein L^(1B) is: C₁-C₆alkyl-NH—.

In embodiment I_(6g), the compounds are of embodiment I₁ having the structure of Formula (Ib), or the compounds are of embodiment I₂, wherein L^(1A) is:

wherein

-   -   w is 1, 2, 3, 4, 5 or 6;     -   ring A₁ is heterocyclic; and     -   L^(1B) is a divalent linker.

In embodiment I_(6h), the compounds are of embodiment I_(6a) wherein L^(1B) is: C₁-C₆alkyl-NH—.

In embodiment I_(6i), the compounds are of embodiment I₁ having the structure of Formula (Ib), or the compounds are of embodiment I₂, wherein L^(1A) is:

wherein

-   -   x is 0, 1, 2, 3, 4, 5 or 6;     -   w is 1, 2, 3, 4, 5 or 6; and     -   ring A₁ is heterocyclic.

In embodiment I_(6j), the compounds are of embodiment I₁ having the structure of Formula (Ib), or the compounds are of embodiment I₂, wherein L^(1A) is:

wherein

-   -   w is 1, 2, 3, 4, 5 or 6; and     -   ring A₁ is heterocyclic.

In embodiment I_(6k), the compounds are of embodiment I₁ having the structure of Formula (Ib), or the compounds are of embodiment I₂, wherein L^(1A) is:

wherein

-   -   w is 1, 2, 3, 4, 5 or 6; and     -   ring A₁ is heterocyclic.

In embodiment I_(6l), the compounds are of any of embodiments I_(6a)-I_(6e), wherein w is selected from one of the following groups (4a)-(4p):

(4a) 1, 2, 3, 4, 5 or 6. (4b) 1, 2, 3, 4 or 5. (4c) 1, 2, 3 or 4. (4d) 1, 2 or 3. (4e) 1 or 2. (4f) 2, 3, 4, 5 or 6. (4g) 2, 3, 4 or 5. (4h) 2, 3 or 4. (4i) 2 or 3 (4j) 3 or 4. (4k) 1. (41) 2. (4m) 3. (4n) 4. (4o) 5. (4p) 6.

In embodiment I_(6m), the compounds are of embodiment I₁ having the structure of Formula (Ib), or the compounds are of embodiment I₂, wherein L^(1A) is:

In embodiment I_(6n), the compounds are of embodiment I₁ having the structure of Formula (Ib), or the compounds are of embodiment I₂, wherein L^(1A) is:

In embodiment I_(6o), the compounds are of embodiment I₁ having the structure of Formula (Ib), or the compounds are of embodiment I₂, wherein L^(1A) is:

In embodiment I₇, the compounds of embodiment I₁ have the structure of Formula (Ic):

wherein

-   -   w is 1, 2, 3, 4, 5 or 6;     -   ring A₁ is heterocyclic; and     -   L^(1B) is a divalent linker.

In embodiment I₈, the compounds of embodiment I₁ have the structure of Formula (Ic′):

wherein

-   -   w is 1, 2, 3, 4, 5 or 6;     -   ring A₁ is heterocyclic; and     -   L^(1B) is a divalent linker.

In embodiment I₉, the compounds of embodiment I₁ have the structure of Formula (Ic):

wherein

-   -   w is 1, 2, 3, 4, 5 or 6;     -   ring A₁ is heterocyclic; and     -   L^(1B) is a divalent linker.

In embodiment I₁₀, the compounds of embodiment I₁ have the structure of Formula (Id):

wherein

-   -   y is 2, 3, 4, 5 or 6;     -   w is 1, 2, 3, 4, 5 or 6;     -   ring A₁ is heterocyclic; and     -   L^(1B) is a divalent linker.

In embodiment I₁₁, the compounds of embodiment I₁ have the structure of Formula (Id′):

wherein

-   -   y is 2, 3, 4, 5 or 6;     -   w is 1, 2, 3, 4, 5 or 6;     -   ring A₁ is heterocyclic; and     -   L^(1B) is a divalent linker.

In embodiment I₁₂, the compounds of embodiment I₁ have the structure of Formula (Id″):

wherein

-   -   y is 2, 3, 4, 5 or 6;     -   w is 1, 2, 3, 4, 5 or 6;     -   ring A₁ is heterocyclic; and     -   L^(1B) is a divalent linker.

In embodiment I₁₃, the compounds of embodiment I₁ have the structure of Formula (Ie):

wherein

x is 0, 1, 2, 3, 4, 5 or 6; and

y is 2, 3, 4, 5 or 6.

In embodiment I_(13′), the compounds of embodiment I₁ have the structure of Formula (Ie) wherein x is 3.

In embodiment I₁₄, the compounds of embodiment I₁ have the structure of Formula (If):

wherein y is 2, 3, 4, 5 or 6.

In embodiment I_(14′), the compounds of embodiment I₁ have the structure of Formula (If) wherein x is 3.

In embodiment I₁₅, the compounds of embodiment I₁ have the structure of Formula (Ig):

wherein y is 2, 3, 4, 5 or 6.

In embodiment I_(15′), the compounds of embodiment I₁ have the structure of Formula (Ig) wherein x is 3.

In embodiment I₁₆, the compounds of embodiment I₁ have the structure of Formula (Ih):

wherein y is 2, 3, 4, 5 or 6.

In embodiment I₁₇, the compounds are of any of embodiments I₁-I₉, wherein y is 4.

In embodiment I₁₈, the compounds are of any of embodiments I₁-I₁₀, wherein R is a chelating agent optionally chelating a therapeutic radioisotope or a PET-active, SPECT-active, or MRI-active radioisotope. The chelating agent can comprise any chelator known in the art, see, e.g., Parus et al., “Chemistry and bifunctional chelating agents for binding (177)Lu,” Curr Radiopharm. 2015; 8(2):86-94; Wangler et al., “Chelating agents and their use in radiopharmaceutical sciences,” Mini Rev Med Chem. 2011 October; 11(11):968-83; Liu, “Bifunctional Coupling Agents for Radiolabeling of Biomolecules and Target-Specific Delivery of Metallic Radionuclides,” Adv Drug Deliv Rev. 2008 September; 60(12): 1347-1370. Specific examples include, for example:

Chelator Structure R DOTA

DOTA-NHS

p-SCN- Bn-NOTA

p-SCN- Bn-PCTA

p-SCN-Bn- Oxo-DO3A

desferriox- amine-p-SCN

Diethylene- triamine- pentaacetic acid (DTPA)

1,4,8,11- tetraazacyclo- tetradecane- 1,4,8,11- tetraacetic acid (TETA)

N,N′-Di(2- hydroxy- benzyl)ethylene- diamine-N,N′- diacetic acid (HBED)

4-(4,7-bis(2- (tertbutoxy)- 2-oxoethyl)- 1,4,7-triaza- cyclononan- 1-yl)-5-(tert- butoxy)-5- oxopentanoic acid (NODAG)

2,2'-(1,4,8,11- tetraaza- bicyclo- [6.6.2]hexa- decane-4,11- diyl)diacetic acid (CB-TE2A)

6-amino-2-(11- (phosphono- methyl)- 1,4,8,11- tetraaza- bicyclo- [6.6.2]hexa- decan-4-yl)- hexanoic acid (CB-TE1K1P)

For example, in embodiment I_(18a), R can be DOTA, bonded through any of its four carboxylic acid groups:

In embodiment I_(18b), R can be

In embodiment I_(18c), R can be

In embodiment I_(18a), can be

In embodiment I_(18e), R can be

In embodiment I_(18f), R can be

In embodiment I_(18g), R can be

In embodiment I_(18h), R can be

In embodiment I_(18i), R can be

In embodiment I_(18j), R can be

In embodiment I_(18k), R can be

In embodiment I_(18i), R can be

If necessary, additional bifunctional chelators can also be readily prepared using literature procedures.

In embodiment I₁₉, each of the preceding compounds may be chelated with a therapeutic radioisotope or a PET-active, SPECT-active, or MRI-active radioisotope selected from ⁶⁸Ga, ⁶⁴Cu, ⁸⁹Zr, ^(186/188)Re, ⁹⁰Y, ¹⁷⁷Lu, ¹⁵³Sm, ²¹³Bi, ²²⁵Ac, and ²²³Ra.

In embodiment I_(19a), each of the preceding compounds may be chelated with a therapeutic radioisotope or a PET-active, SPECT-active, or MRI-active radioisotope that is ⁸⁹Zr.

In embodiment I_(19b), each of the preceding compounds may be chelated with a therapeutic radioisotope or a PET-active, SPECT-active, or MRI-active radioisotope that is ⁶⁴CU.

In embodiment I_(19e), each of the preceding compounds may be chelated with a therapeutic radioisotope or a PET-active, SPECT-active, or MRI-active radioisotope that is with ⁶⁸Ga.

In embodiment I_(19a), each of the preceding compounds may be chelated with a therapeutic radioisotope or a PET-active, SPECT-active, or MRI-active radioisotope that is 186/188Re.

In embodiment I_(19e), each of the preceding compounds may be chelated with a therapeutic radioisotope or a PET-active, SPECT-active, or MRI-active radioisotope that is ⁹⁰Y.

In embodiment I_(19f), each of the preceding compounds may be chelated with a therapeutic radioisotope or a PET-active, SPECT-active, or MRI-active radioisotope that is ¹⁷⁷Lu.

In embodiment I_(19g), each of the preceding compounds may be chelated with a therapeutic radioisotope or a PET-active, SPECT-active, or MRI-active radioisotope that is 153Sm.

In embodiment I_(19h), each of the preceding compounds may be chelated with a therapeutic radioisotope or a PET-active, SPECT-active, or MRI-active radioisotope that is ²¹³Bi.

In embodiment I_(19i), each of the preceding compounds may be chelated with a therapeutic radioisotope or a PET-active, SPECT-active, or MRI-active radioisotope that is ²²⁵Ac.

In embodiment I_(19j), each of the preceding compounds may be chelated with a therapeutic radioisotope or a PET-active, SPECT-active, or MRI-active radioisotope that is ²²³Ra.

In embodiment I₂₀, the compounds are of any of embodiments I₁-I_(19j), wherein R¹ and R² are independently selected from one of groups (5a)-(5o):

-   -   (5a) hydrogen, C₁-C₆ alkyl or a protecting group.     -   (5b) hydrogen or C₁-C₆ alkyl.     -   (5c) C₁-C₆ alkyl or a protecting group.     -   (5d) C₁-C₆ alkyl     -   (5e) hydrogen or a protecting group.     -   (5f) hydrogen.     -   (5g) a protecting group     -   (5h) Any of groups (5a)-(5d), where C₁-C₆alkyl is methyl, ethyl,         n-propyl, iso-propyl, n-butyl, sec-butyl, tert-butyl, n-pentyl         or n-hexyl.     -   (5i) Any of groups (5a)-(5d), where C₁-C₆alkyl is methyl, ethyl,         n-propyl, iso-propyl, n-butyl, sec-butyl or tert-butyl.     -   (5j) Any of groups (5a)-(5d), where C₁-C₆alkyl is methyl, ethyl,         n-propyl or tert-butyl.     -   (5k) Any of groups (5a)-(5d), where C₁-C₆alkyl is methyl, ethyl         or tert-butyl.     -   (5l) Any of groups (5a)-(5d), where C₁-C₆alkyl is methyl or         ethyl.     -   (5m) Any of groups (5a)-(5d), where C₁-C₆alkyl is methyl.     -   (5n) Any of groups (5a)-(5d), where C₁-C₆alkyl is ethyl.     -   (5o) Any of groups (5a)-(5g), where C₁-C₆alkyl is tert-butyl.

A “protecting group” as used herein include, but are not limited to, optionally substituted benzyl, t-butyl ester, allyl ester, alkyl esters (e.g., methyl, ethyl), fluorenylmethoxycarbonyl groups (Fmoc), and amino, carboxylic acid and phosphorus acid protecting groups described in Greene's Protective Groups in Organic Synthesis, 4th Edition (which is incorporated by reference). In some embodiments, R¹ is a carboxylic acid protecting group (e.g., a methyl or t-butyl ester). In some embodiments, R² is a nitrogen protecting group (e.g., Boc, or benzyl).

Optionally benzyl groups include, but are not limited to, unsubstituted benzyl, triphenylmethyl (trityl), diphenylmethyl, o-nitrobenzyl, 2,4,6-trimethylbenzyl, p-bromobenzyl, p-nitrobenzyl, p-methoxybenzyl (PMB), 2,6-dimethoxybenzyl, 4-(methylsulfinyl)benzyl, 4-sulfobenzyl, 4-azidomethoxybenzyl, and piperonyl, and benzyl protecting groups for carboxylic and phosphorus acids disclosed in Greene's Protective Groups in Organic Synthesis (the relevant parts of which are incorporated by reference).

In embodiment I₂₁, the compound of Formula (I) may be selected from the following:

or a pharmaceutically acceptable salt thereof.

In embodiment I₂₂, the present disclosure provides a pharmaceutical composition comprising a compound of Formula (I) and a pharmaceutically acceptable carrier.

In embodiment I₂₃, the present disclosure provides a method for imaging one or more prostate cancer cells in a patient comprising administering to the patient a compound of Formula (I) or a pharmaceutical composition thereof. The method may further include imaging the compound of Formula (I) in vivo. The imaging can be performed with any PET-imaging techniques known in the art.

In embodiment II₁ of this aspect, the disclosure provides compounds of formula (II):

or a pharmaceutically acceptable salt thereof, wherein

-   -   L¹ and L² are independently a divalent linking group;     -   ring B is heterocyclic; and     -   each R¹ and R² are independently hydrogen, C₁-C₆ alkyl or a         protecting group.

In embodiment II₂, L¹, L², R¹ and R² are as described above.

In embodiment II₃, the compounds of embodiment II₁ have the structure of formula (IIa):

or a pharmaceutically acceptable salt thereof.

In embodiment II₄, the compounds of embodiment II₁ have the structure of formula (IIb):

or a pharmaceutically acceptable salt thereof, wherein y is 2, 3, 4, 5 or 6.

In embodiment II_(4a), the compounds are of embodiment II₄ wherein ring B is:

In embodiment II₅, the compounds of embodiment II₁ have the structure of formula (IIc):

or a pharmaceutically acceptable salt thereof, wherein y is 2, 3, 4, 5 or 6.

In embodiment II₆, the compounds are of any of embodiments II₁-II₅, wherein y is 4.

In embodiment I₇, the compound of Formula (II) may be

or a pharmaceutically acceptable salt thereof.

In embodiment III₁ of this aspect, the disclosure provides compounds of the structure:

or a pharmaceutically acceptable salt thereof.

In another aspect, the disclosure provides a method for preparing a compound according to Formula (I). Compounds according to the invention can be made using art recognized techniques combined with methods analogous to those disclosed below.

In embodiment IV₁ of this aspect, the disclosure provides a method for preparing a compound according to Formula (I*) or Formula (I), the method comprising reacting an azide- or alkyne-containing chelating agent optionally associated with a PET-active or therapeutic radioisotope with a azide- or alkyne-modified PMSA inhibitor of formula (IV)

wherein

L¹ and L² are independently a divalent linking group;

A^(C1) comprises an azide or alkyne functional group;

each R¹ and R² are independently hydrogen, C₁-C₆ alkyl or a protecting group; and

X is an albumin bind moiety,

provided that when A^(C1) comprises an azide functional group it is reacted with an alkyne-containing chelating agent optionally associated with a PET-active or therapeutic radioisotope, and when A^(C1) comprises an alkyne functional group it is reacted with an azide-containing chelating agent optionally associated with a PET-active or therapeutic radioisotope.

In embodiment IV₂, the azide- or alkyne-modified PMSA inhibitor of embodiment IV₁ has the structure of Formula (IVa):

In embodiment IV₃, the azide- or alkyne-modified PMSA inhibitor of embodiment IV₁ has the structure of Formula (IVb):

In embodiment IV₄, the azide- or alkyne-modified PMSA inhibitor of embodiment IV₁ has the structure of Formula (IVc):

wherein y is 2, 3, 4, 5 or 6.

In embodiment IV₅, the alkyne-modified PMSA inhibitor of embodiment IV₁ has the structure of Formula (IVd):

wherein ring Ac is heterocyclic and w is as described herein.

In embodiment IV₆, the alkyne-modified PMSA inhibitor of embodiment IV₁ has the structure of Formula (IVe):

In embodiment IV₇, the alkyne-modified PMSA inhibitor of embodiment IV₁ has the structure of Formula (IVf):

In embodiment IV₈, the alkyne-modified PMSA inhibitor of embodiment IV₁ has the structure of Formula (IVg):

In embodiment IV₉, the alkyne-modified PMSA inhibitor of embodiment IV₁ has the structure of Formula (IVh):

In embodiment IV₁₀, the alkyne-modified PMSA inhibitor of embodiment IV₁ has the structure of Formula (IVi):

In embodiment IV₁₁, the azide- or alkyne-containing chelating agent optionally associated with a PET-active or therapeutic radioisotope of embodiment V₁ has the structure of Formula (V):

R-L^(1B)A^(C2)   (V)

wherein

-   -   R is a chelating agent optionally associated with a PET-active         or therapeutic radioisotope;     -   L^(1B) is a divalent linker; and     -   A^(C2) is an azide or alkyne.

In embodiment IV₁₂, the azide- or alkyne-containing chelating agent optionally associated with a PET-active or therapeutic radioisotope of embodiment IV₁ has the structure of Formula (Va):

wherein x is 0, 1, 2, 3, 4, 5 or 6.

In embodiment IV₁₃, the azide- or alkyne-containing chelating agent optionally associated with a PET-active or therapeutic radioisotope of embodiment IV₁ has the structure of Formula (V) or Formula (Va), wherein R comprises DOTA, NOTA, PCTA, DO3A, HBED, NODAG, CB-TE2A, CB-TE1K1P or desferrioxamine optionally associated with ⁸⁹Zr, ⁶⁴Cu, ⁶⁸Ga, ^(186/188)Re, ⁹⁰Y, ¹⁷⁷Lu, ¹⁵³Sm, ²¹³Bi, ²²⁵Ac, or ²²³Ra.

In embodiment IV₁₄, the azide- or alkyne-containing chelating agent optionally associated with a PET-active or therapeutic radioisotope of embodiment IV₁ has the structure of Formula (Vb):

In embodiment IV₁₅, the azide- or alkyne-containing chelating agent optionally associated with a PET-active or therapeutic radioisotope of embodiment IV₁ has the structure of Formula (Vc):

In embodiment IV₁₆, the azide-containing chelating agent optionally associated with a PET-active or therapeutic radioisotope of embodiment IV₁ has the structure of Formula (Vd):

In embodiment IV₁₇, the azide-containing chelating agent optionally associated with a PET-active or therapeutic radioisotope of embodiment IV₁ is of Formula (IVd):

and the alkyne-modified PMSA inhibitor of embodiment IV₁ is of Formula (IVi):

In embodiment IV₁₈, the method is of embodiment IV₁₇ wherein

x is 3;

y is 4; and

w is 2.

In embodiment IV₁₉, the method is of embodiment IV₁ wherein the compound of Formula (I) has the structure

the azide-containing chelating agent associated with a PET-active or therapeutic radioisotope has the structure

and the alkyne-modified PMSA inhibitor has the structure

In embodiment VI, the method is of embodiment IV₁ wherein the compound of Formula (I) has the structure

the azide-containing chelating agent associated with a PET-active or therapeutic radioisotope has the structure

and the alkyne-modified PMSA inhibitor has the structure

In embodiment V₁ of this aspect, the disclosure provides a method for preparing a compound of the structure

the method comprising reacting an azide-containing chelating agent optionally associated with a PET-active or therapeutic radioisotope of the structure

with a alkyne-modified PMSA inhibitor of the structure

In embodiment V₂ of this aspect, the disclosure provides a method for preparing a compound of the structure

the method comprising reacting an azide-containing chelating agent associated with a PET-active or therapeutic radioisotope of the structure

with a alkyne-modified PMSA inhibitor of the structure

EXAMPLES Example 1

Preparation of CTT1402

Details of Synthesis:

Step 1: Synthesis of (8S,11S)-methyl 11-(4-(((benzyloxy)carbonyl)amino)butyl)-8-(3-(tert-butoxy)-3-oxopropyl)-2,2-dimethyl-6,9-dioxo-5-oxa-7,10-diaza-2-siladodecan-12-oate (6)

Step a:

To a stirred solution of Glu-(OtBu)-OH (2.089 g, 10.28 mmol) and triethylamine (0.2.15 mL, 15.43 mmol) in 1:1 Dioxane:water (v/v) (31 mL) Teoc-OSu (3.2 g, 12.34 mmol) was added in one portion. The mixture is stirred at room temperature overnight, then diluted with water (15 mL), acidified with 4 N HCl and 1 N HCl, and extracted with ethyl acetate (3×40 mL). The combined organic layers are washed with brine (60 mL), dried with magnesium sulfate, filtered and evaporated to give a crude oil (3.451 g, 96.6% yield) and dried overnight.

Step b:

To the resultant crude solution (3.451, 9.929 mmol) in 20 mL of anh. DMF was added HBTU (3.765 g, 9.929 mmol) in one portion and stirred at room temperature for 30 min under inert atmosphere. After 30 min, to the reaction mixture, a solution of HCl-Lys(Z)-OMe (3.941 g, 11.914 mmol) and diisopropylethylamine (4.323 mL, 24.822 mmol) in 30 mL of anh. DMF was added drop-wise and stirred overnight at room temperature under inert atmosphere. Upon overnight stirring, the reaction mixture was taken up in ethyl acetate (100 mL) and the organic layer was washed with 1 N HCl (2×, 75 mL), followed by 10% NaHCO_(3(aq)) (wt/v) (2×, 75 mL), then brine (1×, 75 mL). The organic layer was dried with magnesium sulfate, filtered and evaporated. The desired compound 6 was obtained via silica chromatography (Silicycle 40 g cartridge) with 1:1 EtOAc:Hex (Rf=0.33) as the eluent (4.698 g, 75.9%; 73.2% over 2 steps).

Step 2: Synthesis of (8S,11S)-methyl 11-(4-aminobutyl)-8-(3-(tert-butoxy)-3-oxopropyl)-2,2-dimethyl-6,9-dioxo-5-oxa-7,10-diaza-2-siladodecan-12-oate (7)

10% Pd/C (0.797 g, 0.751 mmol) was added to a stirring solution of 6 (4.690 g, 7.518 mmol) in 70 mL of methanol at room temperature. The resultant solution was subjected to H_(2(g)) atmosphere with a double-layered ballon and stirred overnight. Upon overnight stirring, the reaction was complete and filtered through a cellite plug and concentrated down to give 7 in quantitative yield (3.670 g, 99.7%).

Step 3: Synthesis of (8S,11S)-methyl 8-(3-(tert-butoxy)-3-oxopropyl)-11-(4-(4-(4-iodophenyl) butanamido)butyl)-2,2-dimethyl-6,9-dioxo-5-oxa-7,10-diaza-2-siladodecan-12-oate (8)

To a solution of 4-(4-iodophenyl)butanoic acid (0.547 g, 1.89 mmol) in 7 mL of anh. DMF was added HBTU (0.716 g, 1.89 mmol) in one portion and stirred at room temperature for 30 min under inert atmosphere. After 30 min, to the reaction mixture, a solution of 7 (0.770 g, 1.57 mmol) and N,N-diisopropylethylamine (0.410 mL, 2.35 mmol) in 8 mL of anh. DMF was added drop-wise and stirred overnight at room temperature under inert atmosphere. Upon overnight stirring, the reaction mixture was taken up in ethyl acetate (100 mL) and the organic layer was washed with 1 N HCl (2×, 75 mL), followed by 10% NaHCO_(3(aq)) (wt/v) (2×, 75 mL), then brine (1×, 75 mL). The organic layer was dried with magnesium sulfate, filtered and evaporated. The desired compound 8 was obtained via silica chromatography (Silicycle 40 g cartridge) with 65% EtOAc:Hex as the eluent (TLC developed with 75% EtOAc:Hex, Rf=0.33 with) (0.905 g, 75.6%).

Step 4: Synthesis of (S)-methyl 2-((S)-2-amino-5-(tert-butoxy)-5-oxopentanamido)-6-(4-(4-iodophenyl)butanamido)hexanoate (9)

1 M TBAF in THE (1.864 mL, 1.864 mmol) was added to at stirring solution of 8 (0.710 g, 0.932) in 9 mL of anhydrous THE at room temperature under inert atmosphere. The resultant solution was heated to 44° C. and stirred until completion, approximately 5 hrs. Upon completion, the reaction was cooled to room temperature and quenched with 5% KHCO_(3(aq)) (wt/v) (15 mL) and extracted with ethyl acetate (2×, 50 mL). The combined organic layers were washed with brine (2×, 25 mL), dried with magnesium sulfate, filtered and evaporated and the crude was used in the next step without further purification (TLC developed in 20% MeOH:EtOAc, Rf=0.33) (0.5538 g, 96.1%).

Step 5: Synthesis of DBCO-PEG₄-(S)-4-amino-5-(((S)-6-(4-(4-iodophenyl)butanamido)-1-methoxy-1-oxohexan-2-yl)amino)-5-oxopentanoic acid (11)

Step a:

4 N HCl in Dioxane (5.0 mL, 20.08 mmol) was added dropwise to a solution of 9 (0.310 g, 0.502 mmol) in 5.0 mL of anhydrous Dioxane at 4° C. for 30 mins then allowed to warm to room temperature. After 3 hrs, another aliquot of 4 N HCl in Dioxane (2.5 mL, 10.04 mmol) was added at room temp. Upon completion (approximately additional 30 min), the reaction was concentrated down and dried overnight under high vacuum and used in the next step without further purification.

Step b:

DBCO-PEG₄-NHS (0.300 g, 0.462 mmol) in 2 mL of anhydrous Dioxane was added dropwise to the crude carboxylic acid (0.502 mmol) mixture from step 1 and TEA (0.104, 0.753 mmol) in 1.0 mL of anhydrous DMSO and 4 mL of anhydrous Dioxane under inert atmosphere. The resulting solution was stirred overnight. Upon over night stirring, the reaction was taken up in 100 mL of EtOAc and washed with 1 N HCl (50 mL). The combined organic layer was collected and the aqueous layer was back extracted with EtOAc (100 mL). The combined organic layer was dried with MgSO₄, filtered and evaporated down. Compound 11 was isolated with a 0-4% H₂O in 3:7 ACN:MeOH gradient to yield a foamy pinkish orange solid (0.228 g, 41.5%, over 2 steps). m/Z calculated for C₅₂H₆₆IN₅NaO₁₃ [M+Na] 1118.36; found [M+Na] 1118.56 (low-Res MALDI).

Step 6: Synthesis of CTT-1402-OMe

Step a:

EDCI-HCl (0.029 g, 0.153 mmol) followed by N-hydroxysuccinamide (0.014 g, 0.122 mmol) was added to a solution of 11 (0.067 g, 0.061 mmol) in 1.0 mL of anhydrous DMF under inert atmosphere. The reaction was stirred for 1 hr at 50° C. and another aliquot of EDCI-HCl (0.029 g, 0.153 mmol) and N-hydroxysuccinamide (0.014 g, 0.122 mmol) was added and stirred until completion. The crude mixture was diluted with 20 mL of EtOAc and washed with 1 N HCl (aq) to removed unreacted EDCI-HCl. The organic layer was dried through a pad of anhydrous sodium sulfate and concentrated down to yield a glassy pink solid. The solid, 12, was dried under high vacuum for an hr and used in the next step without further purification.

Step b:

Compound 12 in 1 mL of anhydrous DMF was added dropwise to a stirring solution of CTT 1298 (0.419 mL, 0.108 mmol) in 0.839 mL of 1 M TEA-Bicarbonate at 4° C. The resulting solution was stirred overnight at 4° C. The desired compound CTT-1402-OMe was obtained via RP-Prep HPLC with a 10-85% ACN (29.6 mg, 30.9%). Sodium bicarbonate (1.2 eq) was added to neutralize the ammonium acetate in the fractions. The ACN was removed by rotary evaporation with minimal heating, and the remaining water was lyophilized. The yield was determined with a spectrophotometer at 310 nm, ε₃₁₀=11,000 M⁻¹Lcm⁻¹. The purity for CTT-1402 was determined to be greater than 96% by HPLC for all batches based on percent area. large peaks at 4.8 ppm and 1.8 ppm are HOD and Acetate peaks respectively.

Step 7: Synthesis of CTT-1402

CTT-1402-OMe was dissolved in 0.9 mL of MQ water. An aqueous solution of sodium hydroxide (1 N) was added until the pH of the solution was 12.5 and stirred overnight at room temperature. The final compound, CTT-1402, was obtained via RP-Prep HPLC with a 10-85% ACN (16.3 mg, 54.7%). Sodium bicarbonate (1.2 eq) was added to neutralize the ammonium acetate in the fractions. The ACN was removed by rotary evaporation with minimal heating, and the remaining water was lyophilized. The yield was determined with a spectrophotometer at 310 nm, ε₃₁₀=11,000 M⁻¹Lcm⁻¹.

Analytical of CTT1402 (Purity and Identity)

At the penultimate step CTT-1402 was analyzed via ¹H NMR, ³¹P NMR, HRMS-MALDI and HPLC.

HPLC Conditions Analytical HPLC:

Column: Phenomenex Luna 5 um C18(2)

100 Å (cat. No. 00F-4252-E0)

Dimensions: 150×4.6 mm

Wavelength: 310 nM

Percent 10 mM Percent Flow Rate Time NH₄OAc ACN (mL/min) 0.0 90 10 1 5.0 90 10 1 15.0 5 95 1 20.0 5 95 1 22.0 90 10 1 30.0 90 10 1

Prep HPLC:

Column: Phenomenex Luna 10 um C18(2) 100 Å (cat. No. 00B-4253-PO-AX)

Dimensions: 50×21.2 mm

Wavelength: 310 nM

Percent 10 mM Percent Flow Rate Time NH₄OAc ACN (mL/min) 0.0 90 10 15 5.0 90 10 15 20.0 15 85 15 20.1 5 95 15 25.0 5 95 15 25.1 90 10 15 30.0 90 10 15

Analytical HPLC and MS methods were developed to characterize the CTT1402 compound and confirmed the CTT1402 structure and purity as greater than 96%.

Final Structure and Composition of CTT1402

¹H NMR (600 MHz, D₂O) δ 8.46 (s, 1H), 7.51 (d, J=7.7 Hz, 2H), 7.36-7.12 (m, 8H), 7.05 (d, J=7.4 Hz, 2H), 6.70 (d, J=7.8 Hz, 2H), 4.87 (d, J=14.1 Hz, 1H), 4.35 (t, J=7.2 Hz, 1H), 4.13 (dddd, J=17.6, 13.5, 8.7, 4.9 Hz, 3H), 3.76 (q, J=6.3 Hz, 2H), 3.66 (q, J=5.9 Hz, 2H), 3.54-3.40 (m, 12H), 3.31 (d, J=13.9 Hz, 2H), 3.12 (dt, J=31.2, 7.2 Hz, 5H), 3.03-2.93 (m, 2H), 2.48 (d, J=5.9 Hz, 2H), 2.40-2.17 (m, 12H), 2.15-2.04 (m, 4H), 1.88-1.78 (m, 7H), 1.74-1.56 (m, 8H), 1.54-1.40 (m, 5H), 1.36-1.27 (m, 5H). ³¹P NMR (243 MHz, D₂O) δ 7.47. HRMS (MALDI): m/z calculated for C₇₂H₉₈IN₉O₂₅P [M−H] 1646.5456; found 1646.5381.

Preparation of Radiolabeled CTT1403

Solution A: 20 mM CTT1402 in 0.4 M NH₄OAc (pH=7)

Solution B: 5.3 mM DOTA-azide (Macrocyclics, Dallas, Tex., B-288) in 0.4 M NH₄OAc

Solution C: 56 mM gentisic acid in 0.4 M NH₄OAc (pH=7)

Preparation of ¹⁷⁷Lu-DOTA-Azide

Mix solution B (10 μL, 53 nmol DOTA-azide), solution C (10 μL, 0.56 μmol gentisic acid) and ¹⁷⁷LuCl₃ (10 μL, 14.6 mCi) in 0.5 M NH₄OAc buffer (150 μL, pH=4.85). The resulting mixture was heated at 95° C. for 1 h.

For quality control, a small aliquot (1 μL) of the mixture was diluted with 0.5 M NH₄OAc buffer (20 μL, pH=4.85) before injection for HPLC analysis. High radiolabeling yield (>95%), high radiolabeling purity (>95%) and specific activity (10.2 Gbq/μmol) were observed.

HPLC Conditions are listed below:

Time Flow % A % B 0.01 1.00 99.0 1.0 5.00 1.00 99.0 1.0 10.00 1.00 90.0 10.0 14.00 1.00 90.0 10.0 15.00 1.00 99.0 1.0 15.10 0.00 99.0 1.0 Preparation of ¹⁷⁷Lu-CTT1403 for therapy study.

Solution A (17 μL, 0.34 μmol CTT1402) was added to the ¹⁷⁷Lu-DOTA-Azide mixture. The resulting mixture was heated at 37° C. for 1 h before HPLC separation. Fractions containing the highest radio activities were combined and evaporated using nitrogen flow at 42° C. to around 0.41 mL (9.07 mCi). The salt concentration of the remaining solution was adjusted using saline (720 μL).

For quality control, a small aliquot (10 μL) of the mixture was used for HPLC analysis. According to the HPLC results, high conversion rate of 177Lu-DOTA-Azide (>95%), high radiolabeling yield (>95%), and high radiolabeling purity (>95%) were observed.

Time Flow % A % B 0.01 1.00 95.0 5.0 3.00 1.00 95.0 5.0 28.00 1.00 5.0 95.0 32.00 1.00 5.0 95.0 33.00 1.00 95.0 5.0 38.00 1.00 95.0 5.0 38.01 0.00 95.0 5.0

Preparation of Cold Lu-CTT1403 Standard

Solution A: 20 mM CTT1402 in 0.4 M NH₄OAc (pH=7)

Solution B: 5.3 mM DOTA-azide (Macrocyclics, Dallas, Tex., B-288) in 0.4 M NH₄OAc

Solution C: 20 mM LuCl₃ in 0.4 M NH₄OAc (pH=7)

Preparation of Cold Lu-DOTA-Azide

Mix solution B (10 μL, 53 nmol DOTA-azide) and solution C (10 μL, 0.2 μmol LuCl₃) in 0.5 M NH₄OAc buffer (150 μL, pH=4.85). The resulting mixture was heated at 95° C. for 1 h.

Preparation of Cold Lu-CTT1403 Standard

Solution A (17 μL, 0.34 μmol CTT1402) was added to the Lu-DOTA-Azide mixture. The resulting mixture was heated at 37° C. for 1 h before HPLC separation. A small sample was diluted with water for ESI-MS. Found m/z=1165.35408, calcd. for C91H131ILuN17NaO32P2+ m/z (M+H+Na)2+=1165.36282.

CTT1403 without Lu was prepared similarly using DOTA-Azide only.

Analytical of CTT1403 (Purity and Identity)

HPLC Analytical Conditions:

Time Flow % A % B 1 0.01 1.00 95.0 5.0 2 3.00 1.00 95.0 5.0 3 28.00 1.00 5.0 95.0 4 32.00 1.00 5.0 95.0 5 33.00 1.00 95.0 5.0 6 38.00 1.00 95.0 5.0 7 38.01 0.00 95.0 5.0

Final Structure and Composition of CTT1403

CTT1400 was synthesized from CTT1298 with an overall yield of 42.65%

Compound Quantity 0.43M CTT1298 125 μL (25 mg) 1M TEA Bicarb buffer 200 μL 0.26M DBCO-PEG4-NHS 300 μL (50 mg)

CTT1298 was dissolved in ddH₂O to make a 0.43M solution. 125 μL of this solution was added to a 1 mL conical vial. 1M TEA-Bicarb buffer was added to the 1 mL conical vial containing the CTT1298 solution. 1.8 equivalents of DBCO-PEG4-NHS was dissolved in DMSO (to make a 0.26M solution) and added to the vial dropwise. This reaction stirred vigorously overnight at 4° C. The reaction was then purified via prep HPLC and dried down through lyophilization. Before lyophilization, 1.2 equivalents of NaHCO₃ were added to neutralize the pH. The product was quantified by UV absorbance. Confirmation of the desired product was achieved through MS and analytical HPLC methods. Weight: 20.43 mg, yield: 42.65%.

Analytical Analysis of CTT1400 (Purity and Identity)

Analytical HPLC, ¹H & ³¹P NMR, and MS methods were developed to characterize the CTT1400 compound and confirmed the CTT1400 structure and purity was confirmed at >99% for each of the batches produced.

¹H NMR (400 MHz, D₂O) δ 7.45 (d, J=7.4, 1H), 7.36-7.20 (m, 6H), 7.16 (dd, J=7.3, 1.6 Hz, 1H), 4.91 (d, J=14.3 Hz, 1H), 3.95 (ddd, J=13.9, 8.5, 4.9 Hz, 2H), 3.58 (ddd, J=9.6, 5.6, 3.3 Hz, 5H), 3.51-3.38 (m, 12H), 3.33 (dt, J=9.1, 6.2 Hz, 1H), 3.07 ? 2.88 (m, 4H), 2.32 (t, J=6.1 Hz, 2H), 2.26-2.01 (m, 10H), 1.91 (d, J=0.7 Hz, 2H), 1.74-1.60 (m, 4H), 1.62-1.27 (m, 8H), 1.15 (p, J=7.6, 7.1 Hz, 2H). ³¹P NMR (162 MHz, D₂O) δ 7.39. HRMS (MALDI): m/z calculated for C₅₁H₇₂N₆O₂₀P [M+H] 1119.4539; found 1119.4542. HRMS (MALDI) spectrum of CTT1400 Calculated for C₅₁H₇₀N₆O₂₀P⁻ m/z [M−H]=1117.4388; Found m/z=1117.1624.

Final Structure and Composition of Precursor CTT1400

Preparation of Radiolabeled CTT1401¹⁷⁷Lu-labeled DOTA Azide was prepared and combined with CTT1400 to create CTT1401.

-   -   Solution A: 20 mM CTT1400 in 0.4 M NH₄OAc (pH=7)     -   Solution B: 5.3 mM DOTA-azide (Macrocyclics, Dallas, Tex.,         B-288) in 0.4 M NH₄OAc     -   Solution C: 56 mM gentisic acid in 0.4 M NH₄OAc (pH=7)

Solution A (17 μL, 0.34 μmol CTT1400) was added to the ¹⁷⁷Lu-DOTA-Azide mixture. The resulting mixture was heated at 37° C. for 1 h before HPLC separation. ¹⁷⁷Lu-CTT1401 fractions were collected in 200 μL portions. Fractions with the highest radio activities were consolidated into three samples. The first sample (2.24 mCi) was concentrated using nitrogen flow at 41° C. to approximately 130 μL remaining. The mixture was then separated into four tubes (30 μL, 500 μCi). Each tube was diluted with saline to 1.0 mL for injection (50 μCi/100 μL). The second sample (2.22 mCi) was processed similarly to generate another two tubes for injection and quality control HPLC. The last sample (2.49 mCi) was minimized and separated into five tubes. Each tube was adjusted to 250 μL and added sodium ascorbate (3.5 mM), gentisic acid (3.5 mM) and ethanol (10%) to minimize radiolysis. According to the HPLC results, high conversion rate of ¹⁷⁷Lu-DOTA-Azide (>95%), high radiolabeling yield (>95%), and high radiolabeling purity (>95%) were observed.

CTT1401 Cold Standard (Purity and Identity)

HPLC Analytical Conditions

Time Flow % A % B 0.01 1.00 99.0 1.0 5.00 1.00 99.0 1.0 10.00 1.00 90.0 10.0 15.00 1.00 90.0 10.0 25.00 1.00 80.0 20.0 35.00 1.00 80.0 20.0 50.00 1.00 70.0 30.0 55.00 1.00 70.0 30.0 60.00 1.00 1.0 99.0 65.00 1.00 99.0 1.0 70.00 1.00 99.0 1.0 70.01 0.00 99.0 1.0

MS (ESI) of cold CTT1401: Found m/z=1777.4727, calcd. for C₇₀H₁₀₄LuN₁₄O₂₇P⁺ m/z (M+H)⁺=1777.6257. Found m/z=889.2218, calcd. for C₇₀H₁₀₄LuN₁₄O₂₇P²⁺ m/z (M+2H)²⁺=889.3165.

Final Structure and Composition of CTT1401

Purification of Radiotherapeutic Agents with Azide Resin

In order to remove any unlabeled PSMA targeting platforms, the reaction mixtures were applied to a SepPak cartridge packed with an azide-bearing resin. It is expected that all “un-clicked” PSMA targeting platforms will be scavenged by the azide resin. This clean-up step was optimized for efficient removal of the un-clicked PSMA targeting platform without loss of the desired assembled PSMA-targeted radiotherapeutic agents.

Azide-Agarose Resin Study Protocol:

Product Information:

-   -   Company: Click Chemistry Tools     -   Product Name: Azide-Agarose Product No.: 1038     -   Activation Level: 22.0 μmol alkyne groups per mL resin, supplied         in a 50% slurry     -   Support: 6% Cross-linked agarose     -   Bead Size: Spherical, 50-150 m     -   Appearance: Off-white slurry

Preservative: 20% Ethanol in water

Procedure: Dissolve 5 mg DBCO-PEG₄-NHS ester in 800 μL DDH₂O and 200 μL DMSO (to improve solubility). Divide solution into 5 vials, each with 200 μL of solution. Added different amounts of resin to each vial:

Standard=0 μL resin

5 equivalents=350 μL resin

10 equivalents=700 μL resin

15 equivalents=1045 μL resin

20 equivalents=1400 μL resin

Rock vials on a orbital rocker (no stir bars). Remove 15 μL aliquots from each vial after 15, 30, and 60 minutes. Push 15 μL aliquot through a 0.2 m filter that had been activated with methanol. Run all purified samples on the analytical HPLC, with 5 μL injections

% area decrease relative to standard equivalents % decrease at 15 min % decrease at 30 min 5 99.70909513 99.99502675 10 99.99759165 99.99991571 15 99.99954241 99.99997592 20 99.99913299 99.99931362 equivalents % left at 15 min % left at 30 min 5 0.29090487 0.004973247 10 0.002408352 8.42923E−05 15 0.000457587 2.40835E−05 20 0.000867007 0.00068638

This procedure can remove up to 99% of up to 20 equivalents of unreacted NHS ester PSMA scaffold at 30 min and can be used to remove unclicked CTT1402 from radiolabeled final product.

Internalization Studies and Cell Specificity

Uptake and Internalization of CTT1403

The positive control PC3-PIP (PIP) cells, which stably express human PSMA, were compared against a negative control PC3 (PSMA−) cell line. PIP and PC3 cells were seeded separately in 12 well plates (4.0×10⁵ cells/well) and incubated overnight. Cells were washed with internalization buffer (50 mM HEPES, 100 mM NaCl, 1% FBS) ×1 and incubated for 30 min in internalization buffer or internalization buffer with 2 μg 2-PMPA as a blocking agent. Wells were washed ×1 followed by the addition of ¹⁷⁷Lu-CTT1403 (8 ng) and incubated for 15, 30, 60, 120, and 240 min at 37° C. To collect surface bound fractions at each time point, samples were washed ×2 with internalization buffer followed by 10 min incubation with 20 mM sodium acetate in HBSS (pH 4.0). The solution was removed and saved, followed by a wash of 20 mM sodium acetate in HBSS without incubation, and the pooling of the two solutions. The cells were then lysed by rinsing each well with 0.5% SDS in _(dd)H₂O ×2. All samples were counted using a Cobra II automated gamma-counter.

Uptake and internalization of CTT1403 increased over time, with very low nonspecific uptake (see below). Nearly 100% of CTT1403 that bound to target cells were internalized (see table, below). These results indicate that CTT1403 successfully binds to its target on PSMA-expressing cells, is rapidly internalized, and continues to increase beyond 4 hours (FIG. 1).

Time CTT-1403 (min) Surface Internalized Total Ratio Internalized 15 5.29 ± 0.96% 18.67 ± 0.52% 25.13 ± 1.23% 77.03 ± 3.11% 30 8.72 ± 0.52% 31.13 ± 0.63% 41.65 ± 0.92% 77.09 ± 1.13% 120 4.73 ± 0.92% 43.55 ± 4.55% 50.05 ± 3.66% 88.98 ± 2.68% 240 0.39 ± 0.03% 83.43 ± 3.53% 84.65 ± 3.55% 99.17 ± 0.07%

In Vivo Performance of a PSMA-Targeted Radiotherapeutic Platform Containing an Albumin-Binding Motif.

Biodistribution of PSMA-Targeted Radiotherapeutic Agent CTT1403

30 NCr nude mice were injected with 1×10⁶ PC3 (PSMA+) cells subcutaneously in the right shoulder. Tumors were allowed to grow until approximately 0.8 cm across longest axis of measurement (21 days post injection). Mice were injected with 50 μCi (±2 μCi) of ¹⁷⁷Lu-CTT1403 via tail vein. Blocking was performed by pre-treating mice with 2-(phosphonomethyl) pentane-1,5-dioic acid (PMPA) 30 min prior to injection of ¹⁷⁷Lu-CTT1403. Animals were euthanized and tissues harvested at 1 h, 4 h, 4 h (blocked), 24 h, 48 h and 72 h post-injection. In addition, the biodistribution of CTT1403 was also determined at 120 h and 168 h. Blood, kidney, liver, lung, spleen, muscle, heart, bone, tumor, prostate, small intestine, large intestine, stomach and lacrimal glands were harvested. Tissue samples were counted in a gamma counter for 3 min each. Post-weights were taken to determine mass of tissue. Tissue weights and CPM ¹⁷⁷Lu were used to calculate biodistribution.

As a control experiment, 10 NCr nude mice were injected with 1×10⁶ PC3 (PSMA−) cells subcutaneously in the right shoulder. Tumors were allowed to grow until approximately 0.8 cm across longest axis of measurement (34 days post injection). Mice were injected with 50 μCi (±2 μCi) of ¹⁷⁷Lu-CTT1403 tracer via tail vein. Animals were euthanized and tissues harvested at 4 and 24 h post-injection. Blood, kidney, liver, lung, spleen, muscle, heart, bone, tumor, prostate, small intestine, large intestine, stomach and lacrimal glands were harvested. Tissue samples were counted in a gamma counter for 3 min each. Post-weights were taken to determine mass of tissue. Tissue weights and cpm were used to calculate biodistribution (FIG. 2).

¹⁷⁷Lu-CTT1403 showed notable uptake in kidney, lung, prostate, GI tract, lacrimal glands and PC3 (+) tumor. The PC3(−) tumors, which do not express prostate-specific membrane antigen (PSMA), had low to negligible uptake. Normal mouse prostate did show some uptake of the tracer. The tumor and kidney uptake of ¹⁷⁷Lu-CTT1403 are maximum around 48-72 h post-injection, with tumor:background ratios continuing to rise at 72 h. The tumor:kidney ratios for ¹⁷⁷Lu-CTT1403 are 2-4 fold higher than other known tracers. The slower clearance of ¹⁷⁷Lu-CTT1403 is much better aligned to the longer half-life of Lu-177.

Biodistribution Data for ¹⁷⁷Lu-CTT1403 in PC3-PIP Cells:

PC3-PIP (PSMA+) 1 h p.i. 4 h p.i. 24 h p.i. 48 h p.i. 72 h p.i. 4120 h p.i. 168 h p.i. 4 h blocked Blood 25.81 ± 4.22  19.11 ± 3.94  8.63 ± 0.63 5.82 ± 1.57 2.88 ± 0.93 1.25 ± 0.25 0.54 ± 0.14 21.02 ± 2.58  Kidney 12.35 ± 3.24  24.07 ± 9.17  34.13 ± 8.0   52.76 ± 11.54 47.86 ± 12.72 49.13 ± 16.91 34.59 ± 8.60  12.49 ± 3.82  Liver 5.27 ± 1.04 3.74 ± 0.59 1.77 ± 0.24 1.25 ± 0.46 0.61 ± 0.20 0.29 ± 0.09 0.16 ± 0.04 4.09 ± 0.44 Lung 11.13 ± 2.38  8.79 ± 1.33 5.05 ± 0.86 3.56 ± 1.05 1.63 ± 0.62 0.69 ± 0.16 0.35 ± 0.08 10.84 ± 2.34  Spleen 4.69 ± 0.55 4.04 ± 0.51 2.02 ± 0.23 1.49 ± 0.52 0.86 ± 0.31 0.44 ± 0.10 0.29 ± 0.07 4.38 ± 0.43 Muscle 1.86 ± 0.34 1.97 ± 0.36 1.05 ± 0.11 0.69 ± 0.15 0.32 ± 0.09 0.15 ± 0.04 0.06 ± 0.01 2.05 ± 0.28 Heart 7.84 ± 1.31 6.80 ± 1.46 3.11 ± 0.58 2.13 ± 0.59 1.10 ± 0.52 0.49 ± 0.13 0.20 ± 0.09 8.09 ± 1.67 Bone 2.65 ± 0.47 2.60 ± 0.76 1.20 ± 0.11 0.86 ± 0.35 0.43 ± 0.11 0.22 ± 0.04 0.12 ± 0.02 2.35 ± 0.16 Tumor 5.02 ± 0.67 17.38 ± 6.75  37.67 ± 8.66  45.36 ± 6.24  46.48 ± 14.48 35.04 ± 13.23 24.23 ± 4.20  9.28 ± 3.11 Prostate 16.77 ± 5.20  9.35 ± 4.69 6.54 ± 1.69 6.36 ± 3.85 1.88 ± 1.90 0.22 ± 0.05 0.12 ± 0.06 18.61 ± 7.74  Small Intestine 1.05 ± 0.13 1.24 ± 0.43 0.93 ± 0.14 0.69 ± 0.17 0.50 ± 0.15 0.26 ± 0.10 0.33 ± 0.10 1.35 ± 0.39 Large Intestine 2.20 ± 0.31 2.14 ± 0.42 1.20 ± 0.14 0.75 ± 0.21 0.43 ± 0.13 0.33 ± 0.11 0.89 ± 0.22 2.58 ± 0.63 Stomach 0.89 ± 0.11 1.69 ± 0.62 0.90 ± 0.13 0.58 ± 0.20 0.34 ± 0.11 0.24 ± 0.09 0.46 ± 0.17 1.85 ± 0.43 Lacrimal Gland 18.95 ± 5.40  19.69 ± 3.99  10.65 ± 4.63  6.70 ± 2.41 2.98 ± 2.30 0.75 ± 0.12 1.17 ± 0.48 22.36 ± 5.76 

The biodistribution data above indicates that specific tumor uptake of CTT1403 is observed by 4 and 24 hours and that the PSMA negative tumors have minimum uptake. Tumor uptake and kidney uptake is blocked up to 50 using the natural substrate PMPA. PMPA is a reversible inhibitor of PSMA and is not expected to completely block all specific PSMA dependent uptake. It should be noted that unlike human kidney, rodent kidney demonstrates substantial levels of PSMA expression and kidney clearance kinetics is somewhat obscured by this specific PSMA uptake.

Biodistribution to normal tissues and PSMA + Tumors Tumor % ID/g at 4 hrs  3.00 +/− 0.84  17.38 +/− 6.75 Tumor % ID/g at 4 hrs blocked  1.12 +/− 0.17  9.28 +/− 3.11 with PMPA Tumor % ID/g at 72 hrs  0.98 +/− 0.08  35.47 +/− 7.92 Tumor/Blood (4 hrs) 300.2 +/− 84.39  0.98 +/− 0.58 Tumor/Blood (24 hrs)   211 +/− 51.93  4.35 +/− 0.82 Tumor/Blood (72 hrs)  97.6 +/− 8.47  14.97 +/− 5.39 Tumor/Kidney (4 hrs)  0.46 +/− 0.44  0.83 +/− 0.57 Tumor/Kidney (24 hrs)  0.15 +/− 0.04  1.17 +/− 0.39 Tumor/Kidney (72 hrs)  0.18 +/− 0.11  0.80 +/− 0.33 Tumor/Muscle (4 hrs) 90.72 +/− 59.87  9.25 +/− 5.01 Tumor/Muscle (24 hrs)   211 +/− 51.93  35.94 +/− 7.44 Tumor/Muscle (72 hrs)  97.6 +/− 8.47 133.45 +/− 27.96

CTT1403 tumor uptake continues to increase over time (17% at 4 hrs) reaching a maximum at 48-72 hours post injection (35% at 72 hrs). Over this same time period kidney binding shows the expected clearance. Tumor to blood and tumor to muscle ratios continue to increase over the first 72 hours post injection of CTT1403.

Therapeutic Efficacy of CTT1403 (Single Dose)

Fifteen NCr nude mice were injected with 3×10⁵ PC3 (PSMA+) cells subcutaneously in the right shoulder 7 days before start of the therapy using ¹⁷⁷Lu-CTT1403 (10 mice). Average starting tumor volume at start of treatment was 10-20 mm³. Each mouse was injected with 790 μCi (±10 μCi) of CTT1403 tracer via tail vein. Control mice (2) were injected with saline via tail vein. Body weights and tumor volumes were measured before the injection as day 7 followed by measurements three times per week. The tumor volume (V) was determined according to the equation [V=(π÷6)×L×W×H], where L is the longest axis and W is the perpendicular axis to L, and H is the perpendicular axis to L and W plane. Endpoint criteria were defined as longest axis of measurement of tumor exceeds 1.5 cm or active ulceration of the tumor (FIG. 3). Mouse weights were also recorded but no abnormal changes were observed in any of the weights (no reduction in normal growth).

The therapy experiment was repeated with CTT1403 (purity was increased for this second experiment to 95% [CTT1403 Therapy 2] as compared to 85-90% purity for the first experiment [CTT1403 Therapy]) to confirm results. Fifteen NCr nude mice were injected with 3×10⁵ PC3 (PSMA+) cells subcutaneously in the right shoulder 10 days before start of the therapy using ¹⁷⁷Lu-CTT1403. 8 control animals were injected with only saline via tail vein. 8 mice were injected with 790 μCi (±10 μCi) of ¹⁷⁷Lu-CTT1403 tracer via tail vein. Body weights and tumor volumes were measured before the injection as day 0 followed by measurements three times per week. The tumor volume (V) was determined according to the equation [V=π÷6×L×W×H], where L is the longest axis and W is the perpendicular axis to L, and H is the perpendicular axis to L and W plane. Endpoint criteria were defined as longest axis of measurement of tumor exceeds 1.5 cm or active ulceration of the tumor

The increased tumor uptake observed in the biodistribution experiments for CTT1403 (with the albumin binding motif) translates to superior therapeutic efficacy of CTT1403 in PSMA+ human xenograft tumor models as demonstrated by significantly increased tumor doubling times, 90-95% reduction in tumor volume within the first 3 weeks of tumor growth and 31% increase in median survival time based on the first 1403 treatment experiment (median survival time for the second 1403 treatment experiment is still 100% as of day 42 of the experiment) based on the Kaplan Meier survival plots as demonstrated in FIGS. 5 and 6.

Definitions

As used herein, the term “cell” is meant to refer to a cell that is in vitro, ex vivo or in vivo. In some embodiments, an ex vivo cell can be part of a tissue sample excised from an organism such as a mammal. In some embodiments, an in vitro cell can be a cell in a cell culture. In some embodiments, an in vivo cell is a cell living in an organism such as a mammal.

As used herein, the term “contacting” refers to the bringing together of indicated moieties in an in vitro system or an in vivo system. For example, “contacting” PSMA with a compound includes the administration of a compound described herein to an individual or patient, such as a human, as well as, for example, introducing a compound into a sample containing a cellular or purified preparation containing PSMA.

As used herein, the term “individual” or “patient,” used interchangeably, refers to any animal, including mammals, preferably mice, rats, other rodents, rabbits, dogs, cats, swine, cattle, sheep, horses, or primates, and most preferably humans.

As used herein, the phrase “pharmaceutically acceptable salt” refers to both pharmaceutically acceptable acid and base addition salts and solvates. Such pharmaceutically acceptable salts include salts of acids such as hydrochloric, phosphoric, hydrobromic, sulfuric, sulfinic, formic, toluenesulfonic, methanesulfonic, nitric, benzoic, citric, tartaric, maleic, hydroiodic, alkanoic such as acetic, HOOC—(CH₂)_(n)—COOH where n is 0-4, and the like. Non-toxic pharmaceutical base addition salts include salts of bases such as sodium, potassium, calcium, ammonium, and the like. In certain embodiments, the pharmaceutically acceptable salt is a sodium salt. Those skilled in the art will recognize a wide variety of non-toxic pharmaceutically acceptable addition salts.

Pharmaceutical compositions suitable for parenteral administration, such as, for example, by intraarticular (in the joints), intravenous, intramuscular, intradermal, intraperitoneal, and subcutaneous routes, include aqueous and non-aqueous, isotonic sterile injection solutions, which can contain antioxidants, buffers, bacteriostats, and solutes that render the formulation isotonic with the blood of the intended recipient, and aqueous and non-aqueous sterile suspensions that can include suspending agents, solubilizers, thickening agents, stabilizers, and preservatives. Compositions can be administered, for example, by intravenous infusion, orally, topically, intraperitoneally, intravesically or intrathecally.

The term “alkyl” as used herein, means a straight or branched chain hydrocarbon containing from 1 to 10 carbon atoms, unless otherwise specified. Representative examples of alkyl include, but are not limited to, methyl, ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl, iso-butyl, tert-butyl, n-pentyl, isopentyl, neopentyl, n-hexyl, 3-methylhexyl, 2,2-dimethylpentyl, 2,3-dimethylpentyl, n-heptyl, n-octyl, n-nonyl, and n-decyl. When an “alkyl” group is a linking group between two other moieties, then it may also be a straight or branched chain; examples include, but are not limited to —CH₂—, —CH₂CH₂—, —CH₂CH₂CHC(CH₃)—, —CH₂CH(CH₂CH₃)CH₂—.

The term “heterocyclyl” as used herein, means a monocyclic heterocycle or a bicyclic heterocycle. The monocyclic heterocycle is a 3, 4, 5, 6 or 7 membered ring containing at least one heteroatom independently selected from the group consisting of O, N, and S where the ring is saturated or unsaturated, but not aromatic. The 3 or 4 membered ring contains 1 heteroatom selected from the group consisting of O, N and S. The 5 membered ring can contain zero or one double bond and one, two or three heteroatoms selected from the group consisting of O, N and S. The 6 or 7 membered ring contains zero, one or two double bonds and one, two or three heteroatoms selected from the group consisting of O, N and S. The monocyclic heterocycle is connected to the parent molecular moiety through any carbon atom or any nitrogen atom contained within the monocyclic heterocycle. Representative examples of monocyclic heterocycle include, but are not limited to, azetidinyl, azepanyl, aziridinyl, diazepanyl, 1,3-dioxanyl, 1,3-dioxolanyl, 1,3-dithiolanyl, 1,3-dithianyl, imidazolinyl, imidazolidinyl, isothiazolinyl, isothiazolidinyl, isoxazolinyl, isoxazolidinyl, morpholinyl, oxadiazolinyl, oxadiazolidinyl, oxazolinyl, oxazolidinyl, piperazinyl, piperidinyl, pyranyl, pyrazolinyl, pyrazolidinyl, pyrrolinyl, pyrrolidinyl, tetrahydrofuranyl, tetrahydrothienyl, thiadiazolinyl, thiadiazolidinyl, thiazolinyl, thiazolidinyl, thiomorpholinyl, 1,1-dioxidothiomorpholinyl (thiomorpholine sulfone), thiopyranyl, and trithianyl. The bicyclic heterocycle is a monocyclic heterocycle fused to either a phenyl, a monocyclic cycloalkyl, a monocyclic cycloalkenyl, a monocyclic heterocycle, or a monocyclic heteroaryl. The bicyclic heterocycle is connected to the parent molecular moiety through any carbon atom or any nitrogen atom contained within the monocyclic heterocycle portion of the bicyclic ring system. Representative examples of bicyclic heterocyclyls include, but are not limited to, 2,3-dihydrobenzofuran-2-yl, 2,3-dihydrobenzofuran-3-yl, indolin-1-yl, indolin-2-yl, indolin-3-yl, 2,3-dihydrobenzothien-2-yl, decahydroquinolinyl, decahydroisoquinolinyl, octahydro-1H-indolyl, and octahydrobenzofuranyl. Heterocyclyl groups are optionally substituted with one or two groups which are independently oxo or thia. In certain embodiments, the bicyclic heterocyclyl is a 5 or 6 membered monocyclic heterocyclyl ring fused to phenyl ring, a 5 or 6 membered monocyclic cycloalkyl, a 5 or 6 membered monocyclic cycloalkenyl, a 5 or 6 membered monocyclic heterocyclyl, or a 5 or 6 membered monocyclic heteroaryl, wherein the bicyclic heterocyclyl is optionally substituted by one or two groups which are independently oxo or thia.

The term “oxo” as used herein means a ═O group.

The term “saturated” as used herein means the referenced chemical structure does not contain any multiple carbon-carbon bonds. For example, a saturated cycloalkyl group as defined herein includes cyclohexyl, cyclopropyl, and the like.

The term “thia” as used herein means a ═S group.

The term “unsaturated” as used herein means the referenced chemical structure contains at least one multiple carbon-carbon bond, but is not aromatic. For example, a unsaturated cycloalkyl group as defined herein includes cyclohexenyl, cyclopentenyl, cyclohexadienyl, and the like. 

1. A compound of Formula (I*)

or a pharmaceutically acceptable salt thereof, wherein L¹ and L² are independently a divalent linking group; R is a chelating agent optionally chelating a therapeutic radioisotope or a PET-active, SPECT-active, or MRI-active radioisotope; each R¹ and R² are independently hydrogen, C₁-C₆ alkyl or a protecting group; R³ represents hydrogen; and X is an albumin bind moiety.
 2. (canceled)
 3. (canceled)
 4. (canceled)
 5. (canceled)
 6. (canceled)
 7. (canceled)
 8. The compound of claim 1, wherein the compound is of the formula (Ie):

wherein x is 0, 1, 2, 3, 4, 5 or 6; and y is 2, 3, 4, 5 or
 6. 9. (canceled)
 10. (canceled)
 11. (canceled)
 12. (canceled)
 13. The compound of claim 1 that is:


14. A pharmaceutical composition comprising a compound of claim 1 and a pharmaceutically acceptable carrier.
 15. A method for imaging one or more prostate cancer cells in a patient comprising administering to the patient a compound of claim
 1. 16. A method for preparing a compound of claim 1 or pharmaceutically acceptable salt thereof,

the method comprising reacting an azide- or alkyne-containing chelating agent optionally associated with a PET-active or therapeutic radioisotope with a azide- or alkyne-modified PMSA inhibitor of formula (IV)

wherein

comprises an azide or alkyne; each R¹ and R² are independently hydrogen, C₁-C₆ alkyl or a protecting group; and X is an albumin bind moiety, provided that when A^(C1) comprises an azide functional group it is reacted with an alkyne-containing chelating agent optionally associated with a PET-active or therapeutic radioisotope, and when A^(C1) comprises an alkyne functional group it is reacted with an azide-containing chelating agent optionally associated with a PET-active or therapeutic radioisotope.
 17. The method of claim 16, wherein the azide- or alkyne-modified PMSA inhibitor has the structure of Formula (IVa):


18. The method of claim 16, wherein the alkyne-modified PMSA inhibitor has the structure of Formula (IVh):


19. The method of claim 16, wherein the alkyne-modified PMSA inhibitor has the structure of Formula (IVi):


20. The method of any of claim 16, wherein the azide- or alkyne-containing chelating agent optionally associated with a PET-active or therapeutic radioisotope of embodiment IV₁ has the structure of Formula (V): R-L^(1B)-A^(C2)   (V) wherein R is a chelating agent optionally associated with a PET-active or therapeutic radioisotope; L^(1B) is a divalent linker; and A^(C2) is an azide or alkyne.
 21. The method of any of claim 16, wherein the azide- or alkyne-containing chelating agent optionally associated with a PET-active or therapeutic radioisotope of embodiment IV₁ has the structure of Formula (Va):

wherein R is a chelating agent optionally associated with a PET-active or therapeutic radioisotope, A^(C2) is an azide or alkyne, and x is 0, 1, 2, 3, 4, 5 or
 6. 22. The method of claim 21, wherein R comprises DOTA, NOTA, PCTA, DO3A, HBED, NODAG, CB-TE2A, CB-TE1K1P or desferrioxamine optionally associated with ⁸⁹Zr, ⁶⁴Cu, ⁶⁸Ga, ^(186/188)Re, ⁹⁰Y, ¹⁷⁷Lu, ¹⁵³Sm, ²¹³Bi, ²²⁵Ac, or ²²³Ra.
 23. The method of any claim 16, wherein the azide- or alkyne-containing chelating agent optionally associated with a PET-active or therapeutic radioisotope has the structure of Formula (Vb):


24. The method of any of claim 16, wherein the azide-containing chelating agent optionally associated with a PET-active or therapeutic radioisotope has the structure of Formula (Vd):

and the alkyne-modified PMSA inhibitor is of Formula (IVi):


25. The method of claim 23, wherein the azide- or alkyne-containing chelating agent is associated with ⁸⁹Zr, ⁶⁴Cu, ⁶⁸Ga, ^(186/188)Re, ⁹⁰Y, ¹⁷⁷Lu, ¹⁵³Sm, ²¹³Bi, ²²⁵Ac, or ²²³Ra.
 26. A compound of the formula:

wherein L¹ and L² independently represent a divalent linking group; each R¹ and R² is independently hydrogen, C₁-C₆ alkyl or a protecting group; R³ represents hydrogen; and w is 1, 2, 3, 4, 5 or
 6. 27. A compound according to claim 26, which is


28. A compound of the formula:

wherein R¹ is hydrogen, C₁-C₆ alkyl or a protecting group; and R¹⁰ represents hydroxy or a group of the formula


29. A compound according to claim 28, which is


30. A compound according to claim 28, which is 